I've actually seen this happen with the Business Edition also. Have you
recently changed your System/Windows time? Sometimes if the year is wrong
and you change it, it'll reset.
Anywho, go ahead with the activation and use the phone option. Just let
them know what happened and they'll help you reactivate it.
You can just go through the activation process again, and you may have to
call Microsoft to finish the activation. But, it doesn't cost anything, and
you should be up and running in about 5 minutes.
It happens fairly often with SP1 and other small upgrades. The activation
scheme needs some work in Vista, IMO.
