Thank you everyone, I finally solved it. Thanks to your ideas and a friend.

I wasn't wrong: I needed the same version of SQL and then I had to restore it as a user db. I always tried to restore it as the master db

Here goes:

RESTORE DATABASE mastercopy FROM DISK = N'C:\DBback\master'

WITH MOVE N'master' TO N'C:\DBback\mastercopy.mdf',

MOVE N'mastlog' TO N'C:\DBback\mastercopylog.ldf';

GO

That did the job. Now I have a mastercopy DB and I can finally move my tables, records to the new development db.

Thank you for your help!

Regards,

David