We have two ISA 2006 SP1 proxy servers, but they are not in an array. One server is our normal production proxy, and the other is configured as wide 'open' access (for testing and/or when we can't get it to work through the normal proxy). Both proxy's are configured in single NIC mode. The person who primarily handled the configuraion left back in May.
We have recently begun receiving complaints from various users that when they login to specific websites, they receive a page cannot be displayed error instad of the successful login page. The browsers are set through GP to use automatic detect. When we change the proxy setting to use the open proxy, everything works normally.
One of the sites is Facebook. We've recently had a policy change to allow social media for marketing, but we are going through another vendors website to access the FB resources. We only need 3 URL's defined according to that vendor. In the vendors site, part of the screen shows the FB Wall entries. Through the open proxy the wall is displayed, but through the normal proxy it just continues to attempt to load.