ISA error 64 logging in to webpages

[MK-2]

A member of staff mentioned that they can't log in to the TES members area recently. I registered and tested myself and once you click OK after entering login details you get the ISA network error message page come up with the following:

 

Explanation: The request timed out before the page could be retrieved

Technical Information (for support personnel)

Error Code 64: Host not available

Background: The gateway or proxy server lost connection to the Web server.

Date: 03/06/2010 10:37:13

Server: firewall.internal

Source: Remote server

 

I've tried the hotfix from MS that should fix it, but it doesn't. I've also had word that this sometimes affects other sites that are SSL and require you to login.

I've changed the compression setting in ISA (2004) as per another recommendation but it still doesn't work.

It's only one website at the mo but it's driving me mad!

Any help would be appreciated