PRB: Cannot Debug ASP.NET Web Application

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This article was previously published under Q318465

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SYMPTOMS

When you debug an ASP.NET application in Microsoft Visual Studio .NET, you may receive the following Microsoft Development Environment error message:

Error while trying to run project: Unable to start debugging on the web server. The server does not support debugging of ASP.NET or ATL Server applications. Run setup to install the Visual Studio .NET server components. If setup has been run, verify that a valid URL has been specified.

You may also want to refer to the ASP.NET and ATL Server debugging topic in the online documentation. Would you like to disable future attempts to debug ASP.NET pages for this project?

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CAUSE

This error may occur if the Microsoft .NET Framework setup or installation was not completed correctly. When this occurs, the application mappings for ASP.NET file name extensions (such as .aspx) are not configured correctly in Microsoft Internet Information Services (IIS).

To check whether the application mappings are correct, follow these steps:

Click Start, point to Programs, point to Administrative Tools, and then click Internet Services Manager.
Expand the node that corresponds to the local host (computer name), and then expand the Default Web Site node.
Right-click your Web application directory, and then click Properties.
On the Directory tab, under Application Settings, click Configuration.
Click the App Mappings tab.
On the App Mappings tab, under Application Mappings, check whether the .aspx extension is mapped to the following dynamic-link library (DLL):
C:\Windows Directory\Microsoft.Net\Framework\<Version>\aspnet_isapi.dll
NOTE: You must replace Windows Directory in this path with the correct directory for your system and replace Version with the version of the .NET Frame work installed on your system.
If the application mapping entry is not found, follow the steps in the "Resolution" section.

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RESOLUTION

To resolve this problem, use the Aspnet_regiis.exe administration utility that manages the installation and uninstallation of multiple versions of ASP.NET on a single computer.

To use the Aspnet_regiis.exe utility, follow these steps:

Click Start, and then click Run.
Type cmd in the Open box, and then click OK to open a command prompt.
At the command prompt, use the cd command to change to the following directory:
C:\Windows Directory\Microsoft.Net\Framework\Version
Note: You must replace Windows Directory in this path with the correct directory for your system and replace Version with the version of the .NET Frame work installed on your system.
Type aspnet_regiis -i to configure the required application mappings correctly.

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REFERENCES

For additional information about other ASP.NET debugging problems, click the article number below to view the article in the Microsoft Knowledge Base:

306172 (http://support.microsoft.com/kb/306172/EN-US/ ) INFO: Common Errors When You Debug ASP.NET Applications in Visual Studio .NET

For a description of symptoms typically related to ASP.NET and IIS application mappings that are not configured properly, see Microsoft Knowledge Base article Q325093.

325093 (http://support.microsoft.com/kb/325093/EN-US/ ) PRB: ASP.NET Pages Exhibit Unexpected Behavior Because the Server-Side Code Is Not Processed

For more information about ASP.NET debugging, see the following MSDN Web site:

Debugging ASP.NET Web Applications
http://msdn2.microsoft.com/en-us/library/w2faa92k(vs.71).aspx (http://msdn2.microsoft.com/en-us/library/w2faa92k(vs.71).aspx)

For more general information about ASP.NET, see the following MSDN newsgroup:

microsoft.public.dotnet.framework.aspnet (http://msdn.microsoft.com/newsgroups/default.aspx?query=ASP.NET&dg=&cat=en-us-msdn&lang=en&cr=US&pt=&catlist=774F24A2-F71F-425F-AC2B-DC48AB0DA5C9&dglist=&ptlist=&exp=&sloc=en-us)

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