Error message when a client computer tries to access an FTP site through ISA Server, Microsoft Forefront Threat Management Gateway, Medium Business Edition, or Windows Essential Business Server 2008: "Error Code: 502 Proxy Error"

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SYMPTOMS

Consider the following scenario:

On a client computer, Windows Internet Explorer is configured to connect to the Internet through a Microsoft Internet Security and Acceleration (ISA) Server 2004-based proxy server, through an ISA Server 2006-based proxy server, through Microsoft Forefront Threat Management Gateway, Medium Business Edition, or through Windows Essential Business Server 2008.
You have an FTP server that is configured to reject anonymous or wrong requests.

In this scenario, when the client computer tries to access an FTP site through ISA Server, through Microsoft Forefront Threat Management Gateway, Medium Business Edition, or through Windows Essential Business Server 2008, the client computer may receive an error message that resembles the following:

Error Code: 502 Proxy Error.
The login request was denied. The logon account might have been disabled or logon information might have changed. Log on again to verify that the information was typed correctly. If the problem continues, report the problem to the administrator of the Internet server you are requesting.(12015)

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CAUSE

This issue occurs if ISA Server, Microsoft Forefront Threat Management Gateway, Medium Business Edition, or Windows Essential Business Server 2008 does not send the authentication information to the FTP server in the first request. The FTP server closes the connection if the anonymous authentication information is not received in the first request. ISA Server, Microsoft Forefront Threat Management Gateway, Medium Business Edition, or Windows Essential Business Server 2008 usually sends the authentication information to an FTP site in the first request.

Note If you monitor FTP traffic, you may see an entry that resembles the following when the connection fails:

Port: 21
	ftp	Failed Connection Attempt
	User: anonymous
	Request:GET ftp://FTP_Server

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RESOLUTION

To resolve this issue, log on to the FTP server by including a user name and a password in the URL. Use the following format:

ftp://User_Name:Password@FTP_Server

Note When you follow these steps to log on to a secure FTP site, the user name and the password may be displayed in plain text in the Internet Explorer title bar or status bar.

If you monitor FTP traffic after you log on to the FTP Server by using this format, you may see an entry that resembles the following:

Port:21
	ftp	Allowed
	User: anonymous
	Request:GET
	ftp://User_Name:*****@ FTP_Server /

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MORE INFORMATION

For more information about how to set the password that is used when FTP mediates anonymous requests by using the WebProxyFtpClientPassword property, visit the following Microsoft Web site:

http://msdn2.microsoft.com/en-us/library/ms826273.aspx (http://msdn2.microsoft.com/en-us/library/ms826273.aspx)

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