I seem to recall encountering something very similar - turns out M$, in their usual manner, had improved, what they choose to call, security between Win2K Server & Win2K3 Server without too much fuss i.e. notification of such changes to us mere users.

The upgrade automatically installed the improvements - presumably to try and ensure that it [the upgrade] didn't go too smoothly - all too successful in my/our experience.

I shouldn't have been at all surprised at the eventual outcome ... but was - IIRC it took a couple of days to find and provide a reliable fix for the problem - sadly, the details of which were, other than an unhealthy quantity of expletives, retained by the administrator.

I dare say some of you other regular visitors to this place of learning may have noticed a certain dislike of M$ from my POV - the above may provide a little background to my disposition...