Microsoft has released an update for HTTP issues in Microsoft Internet Security and Acceleration (ISA) Server 2004 Service Pack 2 (SP2). This update corrects the problems that are described in the following Microsoft Knowledge Base articles:
915045 (http://support.microsoft.com/kb/915045/) Error message when you try to access a Web site from a Web browser client that is located behind a computer that is running ISA Server 2004 with SP2: "Error Code: 502 Proxy Error"
915421 (http://support.microsoft.com/kb/915421/) Error message when a Web browser tries to access external Web sites from behind an ISA Server 2004 computer that has Service Pack 2 installed
915422 (http://support.microsoft.com/kb/915422/) Some content is unavailable when a user or a program tries to access a Web site through a computer that is running ISA Server 2004 Service Pack 2
916573 (http://support.microsoft.com/kb/916573/) Error message in OWA when you try to download a .zip file from a server that is running ISA Server 2004 Service Pack 2: "500 Internal Server Error. Not implemented (-2147467263)"
917134 (http://support.microsoft.com/kb/917134/) The "Background Intelligent Transfer Service" option is incorrectly available for any non-Microsoft Update cache rule that you create in ISA Server 2004
For details on the fix and how to obtain it, check out: http://support.microsoft.com/kb/916106/
Thomas W Shinder, M.D.
MVP -- ISA Firewalls