Empty RDX media are not being used

Hello,

on an SBS2011 with BE 2012 SP4 + Hotfix RDX cartrigdes are not being used/ overwritten. BE shows under device information, that it needs more memory. The RDX cartridge is empty (formatted) and about twice as large as the size of the data to back up. BE is able to write on the catridges because it creates the folder veritas\b2d with the Changer.cfg and the Folder.cfg in it.

What did I do to this point:

-manually removed remaining IMG folders and even formatted the cartridges

-restartet the BE services

-created a seperate backup job to backup a small text file

-checked the credentials

-removed all media from the Backup Exec- and Windows NT-Backup media sets

What is to do next? Any help is appreciated.