If you have recently downloaded and installed Service Pack 2 for MOSS 2007. The release that was available between April 28, 2009 and July 29, 2009 is buggy. A product expiration is activated incorrectly. Refer to http://support.microsoft.com/kb/971620. To check if you have the same symptoms after installation. Go Central administration -> operations, then under Upgrade and Migration click Convert License Type. on the Current License Type if you see the word Trial ("Office SharePoint Server Trial with Enterprise Client Access License ") , you need to install the latest update referred to in the KB article above.
Please note if you running SharePoint in a Multi-server Farm , you need to install the update in all your machines. And yes, you have to restart the servers.