I have an ISA 2006 server that out of no where fails on a newly created DNS entry for a website with out any errors being reported on the server side. The website does have a web rule in place that works with out a hitch until it just doesn't work. The DNS client can be restarted on that server which temporarily fixes the issue from a few hours to days.
The only error message that has been any help is this one. Which is displayed from the users side when it fails.
Technical Information (for support personnel)
" Error Code 11001: Host not found
" Background: This error indicates that the gateway or proxy server could not find the IP address of an upstream (Web) server. This is usually due to a DNS-related error.