After you configure Microsoft Internet Security and Acceleration (ISA) Server 2004 to filter HTTP content based on signatures or on extensions, users in your organization experience the following symptom.
When a user visits certain URLs, that user receives the following error message in the Web browser:
Error Code 502: Proxy error. The parameter is incorrect. (87)
If you remove all signatures and extensions from the HTTP Filter settings, and if you configure the HTTP Filter component to allow all signatures and extensions, you no longer experience this problem.
Note For more information about how to configure the ISA Server 2004 HTTP Filter component, see the "More Information" section.