Question : SBS 2008 strange issue

1 SBS 2008 Standard server handling DNS and DHCP
4 XP Pro 64 Bit clients

Since the rollout several months ago, I have been chasing a very strange intermittent issue where occasionally the client computers cannot access Companyweb and/or get prompted for authentication when opening Outlook 2007.

While on-site on today I changed the IP of the server to troubleshoot a loss of Exchange connectivity over the weekend.
After changing the IP, I experienced the same phenomenon wherein the client computers requested authentication when Outlook was opened.
Upon further investigation, I also found that the DNS resolution was not working properly as I could not ping anything that was not already cached on the client (created a new CNAME record to test).
Rebooting DNS and Exchange services on the server did NOT fix the issue.
I checked Windows Firewall and a rule allowing ANY to DNS UDP and DNS TCP already existed so I tried disabling the firewall service (NOT changing rules, just stopping the service).
This caused all ping activity to fail.
I re-enabled the firewall service and the authentication and DNS resolution issues were immediately fixed.
I double checked this by adding changing the test CNAME that I created earlier, then flushing the DNS cache on the client and pinging the test CNAME again.  It immediately resolved to the (new) correct host.

I suspect the problem will come back again at some later date as it typically does (usually within a few days).  I see no indiciation of any issues in Event Log that would make me even think it was the Firewall, but I had a wierd issue on another SBS 2008 install site where the Panasonic Phone system programming software (installed on the SBS server) doesn't want to connect the first time every time (I just have to try 2 or 3 times then it connects) which I suspected (but have not yet verified) was a firewall issue and which is what made me check the firewall on this particular site.

Any ideas?

Answer : SBS 2008 strange issue

Sounds good let me know.