ISA 2006 Stops listening on published website

[Guus]

Hello,
We have an ISA 2006 STD configuration with several external IP addresses on
which 3 websites are published.
Without any configuration changes one of those websites was suddenly
inaccessable.
After hours of investigating what could be the problem, I configured a
workaround by publishing the same website on another external IP address.
That worked rightaway.

I'm still puzzeled as how it is possible that ISA 2006 stopped handling the
site on the original address. What I could see (with an IP sniffer) was that
requests were coming in at the external interface, but then everything
stopped. No logging in ISA 2006 about denied packets or whatever.

Of cource I wonder if next week my other sites stop working!
At the moment, OWA, mail, RDP, FTP and other WWW sites work fine, but it
still is strange that this can happen.

regards,
Guus