Have you ever received one of the errors below while browsing a web site?
The page cannot be displayed
There is a problem with the page you are trying to reach and it cannot be displayed.
Technical Information (for support personnel) Error Code: 502 Proxy Error. The HTTP message includes an unsupported header or an unsupported combination of headers. (12156)
This could be caused due a response from a web server that begins with a space or tab character in the HTTP Header. If you have ISA Server 2006 SP1 the fix for that is already built in, however you still need to create the registry key described in KB935693. This KB has an example of the HTTP header that was captured using Netmon and how it looks like.
Note: This KB was also reviewed for TMG MBE and also applies to it.
Thanks so much! I had SP1 installed and checked the file versions but did not have the registry key defined.