Deep 7 posted asking why it is that SBS shuts down the server "without warning" when we detect that you are using SBS in violation of the licensing.
In general, because SBS is such a deal (I mean, really, Windows + Exchange for <$1000 USD is pretty good) we needed to make sure people didn't take advantage of our good nature and try to use SBS as a regular server for a good sized company. The restrictions can be found at the SBS FAQ (http://www.microsoft.com/windowsserver2003/sbs/techinfo/overview/generalfaq.mspx).
What we do is if we detect an SBS server in violation we send a warning message to all PCs in the domain that the server is not in compliance, and that we will shut down the server in one hour if the problem is not rectified (we also log an event in the event log).
I can only infer from Deep 7's post that one of the service he/she shut down was the Messenger service, which would explain why you didn't get any warning until the server actually shut down. We try to be as accomodating as possible when putting in hard licensing enforcement, but if you're using SBS for something that's specifically prohibited, there's not a lot I can do to help you.