This would suggest a bad tape drive or bad tape. Specifically if you are only having the problem with one of your drives consistently, then I'd say that drive is the cause of the issue. Run a cleaning tape through it and if it still gives problems then you might need a replacement drive.
Judging by the transcript snips that you provided, I also believe that this is caused by a bad drive or bad media.
Start by looking at the output of the command :
# obtool dumpdev <tape_drive_name>
(replace "<tape_drive_name>" by the name of the drive which was used during the failed job).
Look for any errors or warnings during the date/time the backup job failed. These message usually provide a good idea about the problem that occurred.
Next try the same backup using the same media in another drive to see it the problem reoccurs or not. In case the problem reoccurs, there's a good chance that the media is bad. If the backup succeeds on another drive, then try the same backup using the original drive but with a new media. If the backup fails again on the same drive using new media, you should open a support request with the tape drive vendor. In that case, collect the logs from the tape library (and dump the tape drives is possible).