Let me answer my own question:
I opened SQL Server studio as administrator. I finally was able to do the backup.
But now the restore on the new pc gives me trouble. See error message. "Backup set holds a backup of a database other then the existing..."
I installed the last version of business studio 5.12 on the new pc. I found it on the Gemalto website dated 2010 though. I compared versions old/new PC. They are identical.
I appreciate your help, thanks!
Andreas