From Jim Harrison on the ISAserver.org mailing list:
You can call PSS and ask for the fix for KB 915045. The KB isn’t published yet, but this is the number PSS needs to access the public fix. You must either open a case with them or wait for it so appear on MU (ASAP).
This package fixes the following issues introduced in ISA 2004 Service Pack 2:
“502 Proxy Error. The HTTP Request includes a non-supported header.” (www.delta.com) “500 Internal Server Error; Not implemented (-2147467263)” (OWA zip files) “The server supplied a compressed response although ISA Server did not request compression” (iTunes)
Thomas W Shinder, M.D.
MVP — ISA Firewalls