Win2k Backup failing

Win2k Backup is constantly reporting the following error just after a backup actually starts…

“Error: 4mm DDS does not contain archive media.”

I have a DDS2 DAT drive connected to a Win2k Server. Any tape loaded does appear in the “Free Media Pool” and is succesfully moved to the Application Media Pool (4mm DDS).

Backup will also recognise any used tapes but I still get the same error when trying to use these.

I have tried cleaning the tape drive and replacing it.

Does anyone know why I keep getting this error? And what can I do about it?