If you ever get this message in SharePoint 2007:
The trial period for this product has expired
You may not actually have an expired license. Especially if you have a RTM Standard or Enterprise license for MOSS.
Instead, it could be one of SharePoint's extra-special error messages that really mean this and this. Or something else. Or it's just feeling saucy that day...
...or maybe it's just an expired license.
Update: It ended up being an antivirus program update that caused the issue. The update was uninstalled and the problem disappeared.