Isn't it frustrating that sometimes you can spent hours on a problem, when in fact the solution is right under your nose? Had this yesterday.
While preparing for some major upgrades, including Windows 2003 SP2, I scanned the internet for possible known issues. At that time, I found this article: http://msexchangeteam.com/archive/2007/07/18/446400.aspx, talking about some serious connectivity issues that can occur when installing SP2, depending on the hardware (and corresponding drivers) used, caused by the Scalable Networking pack included with SP2, which will off-load networking tasks to the hardware of the network card, if capable of doing so.
During testing on a virtual environment, we had none of the issues, so the information in the article slipped out of our minds and we did not think of it when we ran into a lot of weird problems at a customers site. It was only after a couple of hours searching on google on different GPO errors, sql errors, isa errors, etc that we came across this article again…mmmm it did sound familiar!
(The article was in fact still laying around on the desk….)