Log file locations

By default, IIS 7.0 and later versions put log files in the following folder:

inetpub\logs\Logfiles

This folder contains separate directories for each World Wide Web website. By default, the log files are created in the directories daily, and the log files are named by using the date. For example, a log file may be named as follows:

exYYMMDD.log

The HTTP status codes

This section describes the HTTP status codes that IIS 7.0 and later versions use.

Note This article does not list every possible HTTP status code as dictated in the HTTP specification. This article includes only the HTTP status codes that IIS 7.0 and later versions can send. For example, a custom Internet Server API (ISAPI) filter or a custom HTTP module can set its own HTTP status code.

1xx - Informational

These HTTP status codes indicate a provisional response. The client computer receives one or more 1xx responses before the client computer receives a regular response.

IIS 7.0 and later versions use the following informational HTTP status codes:

100 - Continue.
101 - Switching protocols.

2xx - Success

These HTTP status codes indicate that the server successfully accepted the request.

IIS 7.0 and later versions use the following success HTTP status codes:

200 - OK. The client request has succeeded.
201 - Created.
202 - Accepted.
203 - Nonauthoritative information.
204 - No content.
205 - Reset content.
206 - Partial content.

3xx - Redirection

These HTTP status codes indicate that the client browser must take more action to fulfill the request. For example, the client browser may have to request a different page on the server. Or, the client browser may have to repeat the request by using a proxy server.

IIS 7.0 and later versions use the following redirection HTTP status codes:

301 - Moved permanently.
302 - Object moved.
304 - Not modified.
307 - Temporary redirect.

4xx - Client error

These HTTP status codes indicate that an error occurred and that the client browser appears to be at fault. For example, the client browser may have requested a page that does not exist. Or, the client browser may not have provided valid authentication information.

IIS 7.0 and later versions use the following client error HTTP status codes:

400 - Bad request. The request could not be understood by the server due to malformed syntax. The client should not repeat the request without modifications.

IIS 7.0 and later versions define the following HTTP status codes that indicate a more specific cause of a 400 error:
- 400.1 - Invalid Destination Header.
- 400.2 - Invalid Depth Header.
- 400.3 - Invalid If Header.
- 400.4 - Invalid Overwrite Header.
- 400.5 - Invalid Translate Header.
- 400.6 - Invalid Request Body.
- 400.7 - Invalid Content Length.
- 400.8 - Invalid Timeout.
- 400.9 - Invalid Lock Token.
401 - Access denied.

IIS 7.0 and later versions define several HTTP status codes that indicate a more specific cause of a 401 error. The following specific HTTP status codes are displayed in the client browser but are not displayed in the IIS log:
- 401.1 - Logon failed.
- 401.2 - Logon failed due to server configuration.
- 401.3 - Unauthorized due to ACL on resource.
- 401.4 - Authorization failed by filter.
- 401.5 - Authorization failed by ISAPI/CGI application.
- 401.501 - Access Denied: Too many requests from the same client IP; Dynamic IP Restriction Concurrent request rate limit reached.
- 401.502 - Forbidden: Too many requests from the same client IP; Dynamic IP Restriction Maximum request rate limit reached.
- 401.503 - Access Denied: the IP address is included in the Deny list of IP Restriction
- 401.504 - Access Denied: the host name is included in the Deny list of IP Restriction
403 - Forbidden.

IIS 7.0 and later versions define the following HTTP status codes that indicate a more specific cause of a 403 error:
- 403.1 - Execute access forbidden.
- 403.2 - Read access forbidden.
- 403.3 - Write access forbidden.
- 403.4 - SSL required.
- 403.5 - SSL 128 required.
- 403.6 - IP address rejected.
- 403.7 - Client certificate required.
- 403.8 - Site access denied.
- 403.9 - Forbidden: Too many clients are trying to connect to the web server.
- 403.10 - Forbidden: web server is configured to deny Execute access.
- 403.11 - Forbidden: Password has been changed.
- 403.12 - Mapper denied access.
- 403.13 - Client certificate revoked.
- 403.14 - Directory listing denied.
- 403.15 - Forbidden: Client access licenses have exceeded limits on the web server.
- 403.16 - Client certificate is untrusted or invalid.
- 403.17 - Client certificate has expired or is not yet valid.
- 403.18 - Cannot execute requested URL in the current application pool.
- 403.19 - Cannot execute CGI applications for the client in this application pool.
- 403.20 - Forbidden: Passport logon failed.
- 403.21 - Forbidden: Source access denied.
- 403.22 - Forbidden: Infinite depth is denied.
- 403.501 - Forbidden: Too many requests from the same client IP; Dynamic IP Restriction Concurrent request rate limit reached.
- 403.502 - Forbidden: Too many requests from the same client IP; Dynamic IP Restriction Maximum request rate limit reached.
- 403.503 - Forbidden: the IP address is included in the Deny list of IP Restriction
- 403.504 - Forbidden: the host name is included in the Deny list of IP Restriction
404 - Not found.

IIS 7.0 and later versions define the following HTTP status codes that indicate a more specific cause of a 404 error:
- 404.0 - Not found.
- 404.1 - Site Not Found.
- 404.2 - ISAPI or CGI restriction.
- 404.3 - MIME type restriction.
- 404.4 - No handler configured.
- 404.5 - Denied by request filtering configuration.
- 404.6 - Verb denied.
- 404.7 - File extension denied.
- 404.8 - Hidden namespace.
- 404.9 - File attribute hidden.
- 404.10 - Request header too long.
- 404.11 - Request contains double escape sequence.
- 404.12 - Request contains high-bit characters.
- 404.13 - Content length too large.
- 404.14 - Request URL too long.
- 404.15 - Query string too long.
- 404.16 - DAV request sent to the static file handler.
- 404.17 - Dynamic content mapped to the static file handler via a wildcard MIME mapping.
- 404.18 - Querystring sequence denied.
- 404.19 - Denied by filtering rule.
- 404.20 - Too Many URL Segments
- 404.501 - Not Found: Too many requests from the same client IP; Dynamic IP Restriction Concurrent request rate limit reached.
- 404.502 - Not Found: Too many requests from the same client IP; Dynamic IP Restriction Maximum request rate limit reached.
- 404.503 - Not Found: the IP address is included in the Deny list of IP Restriction
- 404.504 - Not Found: the host name is included in the Deny list of IP Restriction
405 - Method Not Allowed.
406 - Client browser does not accept the MIME type of the requested page.
408 - Request timed out.
412 - Precondition failed.

5xx - Server error

These HTTP status codes indicate that the server cannot complete the request because the server encounters an error.

IIS and later versions use the following server error HTTP status codes:

500 - Internal server error.

IIS 7.0 and later versions define the following HTTP status codes that indicate a more specific cause of a 500 error:
- 500.0 - Module or ISAPI error occurred.
- 500.11 - Application is shutting down on the web server.
- 500.12 - Application is busy restarting on the web server.
- 500.13 - Web server is too busy.
- 500.15 - Direct requests for Global.asax are not allowed.
- 500.19 - Configuration data is invalid.
- 500.21 - Module not recognized.
- 500.22 - An ASP.NET httpModules configuration does not apply in Managed Pipeline mode.
- 500.23 - An ASP.NET httpHandlers configuration does not apply in Managed Pipeline mode.
- 500.24 - An ASP.NET impersonation configuration does not apply in Managed Pipeline mode.
- 500.50 - A rewrite error occurred during RQ_BEGIN_REQUEST notification handling. A configuration or inbound rule execution error occurred.
  Note Here is where the distributed rules configuration is read for both inbound and outbound rules.
- 500.51 - A rewrite error occurred during GL_PRE_BEGIN_REQUEST notification handling. A global configuration or global rule execution error occurred.
  Note Here is where the global rules configuration is read.
- 500.52 - A rewrite error occurred during RQ_SEND_RESPONSE notification handling. An outbound rule execution occurred.
- 500.53 - A rewrite error occurred during RQ_RELEASE_REQUEST_STATE notification handling. An outbound rule execution error occurred. The rule is configured to be executed before the output user cache gets updated.
- 500.100 - Internal ASP error.
501 - Header values specify a configuration that is not implemented.
502 - Web server received an invalid response while acting as a gateway or proxy.

IIS 7.0 and later versions define the following HTTP status codes that indicate a more specific cause of a 502 error:
- 502.1 - CGI application timeout.
- 502.2 - Bad gateway: Premature Exit.
- 502.3 - Bad Gateway: Forwarder Connection Error (ARR).
- 502.4 - Bad Gateway: No Server (ARR).
503 - Service unavailable.

IIS 7.0 and later versions define the following HTTP status codes that indicate a more specific cause of a 503 error:
- 503.0 - Application pool unavailable.
- 503.2 - Concurrent request limit exceeded.
- 503.3 - ASP.NET queue full
- 503.4 - FastCGI queue full

Common HTTP status codes and the causes

The following table describes the causes of some common HTTP status codes.

Code	Description	Notes
200	OK	IIS 7.0 and later versions successfully processed the request.
304	Not modified	The client browser requests a document that is already in the cache, and the document has not been modified since the document was cached. The client browser uses the cached copy of the document instead of downloading the document from the server.
400	Bad request	The Http.sys file blocks IIS 7.0 and later versions from processing the request because of a problem in the request. Typically, this HTTP status code means that the request contains characters or sequences that are not valid or that the request contradicts the security settings in the Http.sys file.
401.1	Logon failed	The logon attempt is unsuccessful probably because of a user name or a password that is not valid. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942044 Error message when you try to run a web application that is hosted on IIS 7.0: "HTTP Error 401.1 - Not Found"
401.2	Logon failed due to server configuration	This HTTP status code indicates a problem in the authentication configuration settings on the server. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942043 Error message when you try to visit a webpage that is hosted on IIS 7.0: "HTTP Error 401.2 - Unauthorized"
401.3	Unauthorized due to ACL on resource	This HTTP status code indicates a problem in the NTFS file system permissions. This problem may occur even if the permissions are correct for the file that you are trying to access. For example, this problem occurs if the IUSR account does not have access to the C:\Winnt\System32\Inetsrv directory. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942042 Error message when you try to browse a webpage that is hosted on a server that is running IIS 7.0: "HTTP Error 401.3 - Unauthorized"
401.4	Authorization failed by filter	An ISAPI filter does not let the request be processed because of an authorization problem. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942079 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 401.4 - Authorization failed by filter"
401.5	Authorization failed by ISAPI/CGI application	An ISAPI application or a Common Gateway Interface (CGI) application does not let the request be processed because of an authorization problem. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942078 Error message when you visit a website that is hosted on a computer that is running IIS 7.0: "HTTP Error 401.5 - Authorization failed by ISAPI/CGI application"
403.1	Execute access forbidden	The appropriatelevel of the Execute permission is not granted. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942065 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.1 - Forbidden"
403.2	Read access forbidden	The appropriate level of the Read permission is not granted. Verify that you have set up IIS 7.0 and later versions to grant the Read permission to the directory. Additionally, if you use a default document, verify that the default document exists. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942036 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.2 - Forbidden"
403.3	Write access forbidden	The appropriate level of the Write permission is not granted. Verify that the IIS 7.0 and later versions permissions and the NTFS file system permissions are set up to grant the Write permission to the directory. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942035 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.3 - Forbidden"
403.4	SSL required	The request is made over a nonsecure channel, and the web application requires a Secure Sockets Layer (SSL) connection. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942070 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.4 - Forbidden"
403.5	SSL 128 required	The server is configured to require a 128-bit SSL connection. But, the request is not sent by using 128-bit encryption. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942069 Error message when you try to browse a webpage that is hosted on IIS 7.0: "HTTP Error 403.5 - Forbidden"
403.6	IP address rejected	The server is configured to deny access to the current IP address. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942068 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.6 - IP Address Rejected"
403.7	Client certificate required	The server is configured to require a certificate for client authentication. But, the client browser does not have an appropriate client certificate installed. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942067 Error message when you try to run a web application that is hosted on a server that is running IIS 7.0: "HTTP Error 403.7 - Forbidden"
403.8	Site access denied	The server is configured to deny requests based on the Domain Name System (DNS) name of the client computer. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base: 942066 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.8 - Forbidden"
403.12	Mapper denied access	The page that you want to access requires a client certificate. But, the user ID that is mapped to the client certificate is denied access to the file. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942064 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.12 - Client Certificate Denied"
403.13	Client certificate revoked	The client browser tries to use a client certificate that was revoked by the issuing certification authority. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942063 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.13 - Forbidden"
403.14	Directory listing denied	The server is not configured to display a content directory listing, and a default document is not set. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942062 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.14 - Forbidden"
403.16	Client certificate is untrusted or invalid.	The client browser tries to use a client certificate that is not trusted by the server that is running IIS 7.0 and later versions or that is not valid. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942061 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.16 - Forbidden"
403.17	Client certificate has expired or is not yet valid.	The client browser tries to use a client certificate that is expired or that is not yet valid. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942038 Error message when you try to visit a webpage that is hosted on Internet Information Services 7.0: "HTTP Error 403.17 (Forbidden) - The client certificate has expired"
403.18	Cannot execute requested URL in the current application pool.	A custom error page is configured, and the custom error page resides in a different application pool than the application pool of the requested URL. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942037 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.18 - Forbidden"
403.19	Cannot execute CGI applications for the client browser in this application pool.	The identity of the application pool does not have the Replace a process level token user right. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942048 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 403.19 - Forbidden"
404.0	Not found.	The file that you are trying to access was moved or does not exist. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942041 Error message when you try to open a webpage that is hosted on IIS 7.0: "HTTP Error 404.0 - Not Found"
404.2	ISAPI or CGI restriction.	The requested ISAPI resource or the requested CGI resource is restricted on the computer. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942040 Error message when you try to visit a webpage that is hosted on a computer that is running IIS 7.0: "HTTP Error 404.2 – Not Found"
404.3	MIME type restriction.	The current MIME mapping for the requested extension type is not valid or is not configured. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942032 Error message when users visit a website that is hosted on a server that is running Internet Information Services 7.0: "HTTP Error 404.3 - Not Found"
404.4	No handler configured.	The file name extension of the requested URL does not have a handler that is configured to process the request on the Web server. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942052 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.4 - Not Found"
404.5	Denied by request filtering configuration.	The requested URL contains a character sequence that is blocked by the server. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942053 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.5 - URL Sequence Denied"
404.6	Verb denied.	The request is made by using an HTTP verb that is not configured or that is not valid. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942046 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.6 - VERB_DENIED"
404.7	File extension denied.	The requested file name extension is not allowed. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942045 Error message when you try to browse a webpage that is hosted on IIS 7.0: "HTTP Error 404.7 - FILE_EXTENSION_DENIED"
404.8	Hidden namespace.	The requested URL is denied because the directory is hidden. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942047 Error message when you try to visit a webpage that is hosted on IIS 7.0: "HTTP Error 404.8 - HIDDEN_NAMESPACE"
404.9	File attribute hidden.	The requested file is hidden. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942049 Error message when you try to visit a website that is hosted on IIS 7.0: "HTTP Error 404.9 - File Attribute Hidden"
404.10	Request header too long.	The request is denied because the request headers are too long. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942077 Error message when you visit a website that is hosted on a server that is running Internet Information Services 7.0: "HTTP Error 404.10 - REQUEST_HEADER_TOO_LONG"
404.11	Request contains double escape sequence.	The request contains a double escape sequence. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942076 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.11 - URL_DOUBLE_ESCAPED"
404.12	Request contains high-bit characters.	The request contains high-bit characters, and the server is configured not to allow high-bit characters. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942075 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.12 - URL_HAS_HIGH_BIT_CHARS"
404.13	Content length too large.	The request contains a Content-Length header. The value of the Content-Length header is larger than the limit that is allowed for the server. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942074 Error message when you visit a website that is hosted on a server that is running Internet Information Services 7.0: "HTTP Error 404.13 - CONTENT_LENGTH_TOO_LARGE"
404.14	Request URL too long.	The requested URL exceeds the limit that is allowed for the server. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942073 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.14 - URL_TOO_LONG"
404.15	Query string too long.	The request contains a query string that is longer than the limit that is allowed for the server. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942071 Error message when you visit a website that is hosted on a server that is running IIS 7.0: "HTTP Error 404.15 - Not Found"
404.17	Dynamic content mapped to the static file handler.	For more information, click the following article number to view the article in the Microsoft Knowledge Base: 2019689 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 404.17 - Not Found"
405.0	Method not allowed.	The request is made by using an HTTP method that is not valid. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942051 Error message when a user visits a website that is hosted on a server that is running Internet Information Services 7.0: "HTTP Error 405.0 - Method not allowed"
406.0	Invalid MIME type.	The request is made by using an Accept header that contains a MIME value that is not valid. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942050 Error message when you visit a website that is hosted on a server that is running Internet Information Services 7.0: "HTTP Error 406 - Not Acceptable"
412.0	Precondition failed.	The request is made by using an If-Match request header that contains a value that is not valid. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942056 Error message when you visit a website that is hosted on Internet Information Services (IIS) 7.0: "HTTP Error 412 - Precondition failed"
500	Internal server error.	This HTTP status code may occur for many server-side reasons. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942031 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 500.0 - Internal Server Error"
500.11	Application is shutting down on the web server.	The request is not processed because the destination application pool is shutting down. Wait for the worker process to finish shutting down, and then try the request again. If this problem persists, the web application may be experiencing problems that prevent the web application from shutting down correctly.
500.12	Application is busy restarting on the web server.	The request is not processed because the destination application pool is restarting. This HTTP status code should disappear when you refresh the page. If this HTTP status code appears again after you refresh the page, the problem may be caused by antivirus software that is scanning the Global.asa file. If this problem persists, the web application may be experiencing problems that prevent the web application from restarting correctly.
500.13	Web server is too busy.	The request is not processed because the server is too busy to accept any new incoming requests. Typically, this HTTP status code means that the number of incoming concurrent requests exceeds the number that the IIS 7.0 and later versions web application can process. This problem may occur because the performance configuration settings are set too low, the hardware is insufficient, or a bottleneck occurs in the IIS 7.0 and later versions web application. A common troubleshooting method is to generate a memory dump file of the IIS 7.0 and later versions processes when the error is occurring and then to debug the memory dump file.
500.15	Direct requests for Global.asax are not allowed.	A direct request for the Global.asa file or for the Global.asax file is made. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942030 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 500.15 - Direct request for global.asa are not allowed"
500.19	Configuration data is invalid.	This HTTP status code occurs because of a problem in the associated Applicationhost.config file or in the associated Web.config file. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942055 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 500.19 - Internal Server Error"
500.100	Internal ASP error.	An error occurs during the processing of an Active Server Pages (ASP) page. To obtain more specific information about the error, disable friendly HTTP error messages in the web browser. Additionally, the IIS log may show an ASP error number that corresponds to the error that occurs. For more information about ASP error messages and about the meaning of ASP error messages, click the following article number to view the article in the Microsoft Knowledge Base: 294271 ASP error codes
501.0	Not implemented.	The client browser sends an HTTP-Trace verb, and the server is not configured to process the HTTP-Trace verb. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942058 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 501.0 - Not Implemented"
502.1	CGI application timeout.	A CGI application does not return a valid HTTP response in the configured time limit. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942059 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 502.1 - Bad Gateway"
502.2	Bad gateway: Premature Exit	A CGI application returns an HTTP response that is not valid to the server that is running IIS 7.0 and later versions. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 942057 Error message when you visit a website that is hosted on IIS 7.0: "HTTP Error 502.2 - Bad Gateway"
503.0	Service unavailable.	The request is sent to an application pool that is currently stopped or that is currently disabled. To resolve this issue, make sure that the destination application pool is started. The event log may give information about why the application pool is stopped or disabled.
503.2	Concurrent request limit exceeded.	The appConcurrentRequestLimit property is set to a value that is lower than the current number of concurrent requests. IIS 7.0 and later versions do not allow more concurrent requests than the value of the appConcurrentRequestLimit property.

HTTP substatus codes

Added in IIS 8.0

Subcode	Description
400.10	Invalid XFF header
400.11	Invalid WebSocket request

Added in ARR 3.0.1916

Subcode	Description
400.601	Bad client request (ARR)
400.602	Invalid time format (ARR)
400.603	Parse range error (ARR)
400.604	Client gone (ARR)
400.605	Maximum number of forwards (ARR)
400.606	Asynchronous competition error (ARR)

502.2	Map request failure (ARR)
502.3	WinHTTP asynchronous completion failure (ARR)
502.4	No server (ARR)
502.5	WebSocket failure (ARR)
502.6	Forwarded request failure (ARR)
502.7	Execute request failure (ARR)