Hello,
We request you to mention the exact error that you receive?
If you are already using hardware compression then this could happen if the tapes that you are using are old or have been used several times.
we request you to perform a "long erase" operation on the tape that you want to erase and check.
Also perform a full backup until the tape is filled for example if the tape capacity is 30GB then try to perform a backup of 30GB with overwrite option. Once the backup is completed and next time when the tape is inserted for backup, check the media capacity displayed.
Also perform the following:
-Please clean the tape drive according to the hardware manufacturers guidelines.
Please also refer the following technote
http://seer.support.veritas.com/docs/199542.htm
Thanks,
NOTE : If we do not receive your reply within two business days, this post would be marked "assumed answered" and would be moved to "answered questions" pool.