Trying to upgrade/move a MOSS Farm using the database attach you recieve the message:
The specified SPContentDatabase has been upgraded to a newer version of SharePoint. Please upgrade this SharePoint application server before attempting to access this object
But you say, it's the same version or may you did the Slipstream process w/SP2 already and it worked fine?
If you've not run the WSS and MOSS SP2's, do so and it will fix the problem. If you used the Slipstream process outlined by Microsoft - surprise, it's not clear from the document you need to do BOTH WSS and MOSS - install WSS V3.0 SP2 and you'll be off and running.