Via Microsoft SharePoint Team Blog
"During the installation of SP2, a product expiration date is improperly activated. This means SharePoint will expire as though it was a trial installation 180 days after SP2 is deployed. "
Which products are affected by this?
Applying Service Pack 2 to any of the following products will result in this issue: Office SharePoint Server 2007, Office SharePoint Server 2007 for Internet Sites, Project Server 2007, Form Server 2007, Search Server 2008 and Search Server 2008 Express.
Windows SharePoint Services 3.0 is not affected by this issue.
Check out the Microsoft SharePoint Team Blog on what you can do to fix the Service Pack 2 issue.