TABLE 3   WEB PROXY HTTP ERROR CODES
Error	Possible Solution
HTTP/1.0 500 server error (An attempt has been made to operate on an impersonation token by a thread that is not currently impersonating a client)	When changes are made to the WWW service home directory and the Web proxy service is running, this error can occur. Stop and restart the Web proxy and WWW services to correct this problem.
HTTP/1.0 500 server error <number>	This error is indicative of an authentication type mismatch that occurs when Windows NT challenge/response authentication is used to validate Web proxy service clients and the clients are attempting to connect as anonymous or with basic authentication. You may need to set the WWW service authentication to Basic or Allow Anonymous to fix this problem.
HTTP/1.0 500 server error (the specified chapter could not be found)	Check the location of your IIS scripts directory and ensure there’s a Proxy subdirectory at that location. If not, create a scripts directory off the root of your IIS Web site. You may also have to reinstall the proxy server to get the appropriate binary files into the scripts directory.