Hi,
It is really surprising that still few of the clients are depending on offline backups.
We do not take any offline backup for any of SAP systems, we do take online_cons backups which are restorable and recoverable (Because we get very less maintenance windows for SAP environment).....It's a different thing.
On your issue - Have you checked the online backup? I mean online+archive log?
Check and update the status.
Issue seems with your backup drive/media, a test backup of online+archive log can give some hint.
Regards,
Nick Loy