I've installed MOSS 2007 RTM on a couple of test VPCs here, using the 180-day trial version. Everything worked fine until I tried to create a new page in my Publishing Portal - suddenly received a "The trial period for this product has expired" message and it won't let me create it. This is strange, since I got this key from Microsoft Downloads 3 days ago. Switching the server to an MSDN key didn't help either, so it wasn't a licensing issue.
Strangely enough, most MOSS features did work - only a handful, like creating pages and associating a custom VS2005-build Workflow with a document library - caused this error. Other distinctly MOSS-based features like publishing and search worked like a charm.
The first suspect was the fact my server is running on a Domain Controller. Seems there's a well-known problem with running MOSS on a DC, and an official workaround by Microsoft that sets some registry keys and reconfigures the server. This problem, however, should have prevented any site from loading, not only that specific error. And anyway, it didn't help.
What several furious minutes of googling revealed is that this is caused by a server in a farm scenario (even a single-server farm) whose application pools are using non-admin accounts. In my case, it was the default NetworkService and LocalService accounts for the DefaultAppPool, MSSharepointAppPool and OfficeServerApplicationPool pools. When I switched them all to using a domain account with admin rights on the server, everything started working.
So in summary:
1) This error still happens on the RTM release, not just the B2TR release as mentioned in the forum post.
2) I can only assume that this doesn't always happen, since I'm sure testing involved creating a single-server farm with all default settings. I have no idea why it happened./
3) The fix mentioned in the link works perfectly, and is heartily recommended.