Microsoft’s SharePoint team has announced that there is a bug in Service Pack 2 for MOSS that will trigger SharePoint to believe it is a trial instance of the product.  A workaround is supplied by Microsoft:

We are working to release a hotfix to automatically fix this issue. A manual work-around is currently available and involves customers re-entering their Product ID number (PID) on the Convert License Type page in Central Administration.  For more information and detailed steps please read this KB article.

In addition, Microsoft is working on a hotfix to be released shortly.  More information can be found on the Microsoft SharePoint Team Blog:

Microsoft SharePoint Team Blog : Attention: Important Information on Service Pack 2