One of our clients has SQL Server 2008R2 64 bit version running in development.
It recently expired after the evaluation time elapsed. We had a valid licensed copy to upgrade too, yet after performing the upgrade, the message still appeared.
After doing an exhaustive search, I found this article:
Open RegEdit, modified the entry from 1 to 3, closed RegEdit:
Set the Dev Server System Clock to Jan 1, 2013, prior to the expiration date.
Started the Setup.exe for SQL Server Install --> Maintenance --Edition Upgrade:
Next, next... and it's running...
Ran for a while, then completed, all green Success:
Set the clock back to current date:
Went to Services, to start the service, SQL Server and SQL Server Agent:
Opened SQL Server:
And we're in:
And all the previous databases exist in tact, upgraded to the new version, ready for development.
That blog post listed above really saved the day, thanks much!