Read the full disclosure "Attention- Important Information on Service Pack 2" in Microsoft’s SharePoint Blog
There is an issue with installing SP2, which causes your SharePoint environment to fall back to "Evaluation" licence without ever notifying you.
So if you’ve got SP2 recently installed, have a look at your license type to make sure it’s still valid. If it says "Evalutation" – you’ll simply need to insert the original key again.
If you’ve got SP2 installed, read this article: Attention- Important Information on Service Pack 2
Checking out for the weekend!