Error code 84 for nfs mount backup

Call your hardware vendor and show them the TapeAlert codes.

See http://www.t10.org/ftp/t10/document.02/02-142r0.pdf 

0x03:
Hard Error
This flag is set for any unrecoverable read/write/positioning error, and is
internally cleared when the media is ejected (this flag is set as an explanation
of the error in conjunction with one of the recovery action flags 4, 5, or 6)

0x06:
Write Failure
The tape is from a faulty batch or the tape drive is faulty:
1. Use a good tape to test the drive.
2. If the problem persists, call the tape drive supplier helpline.

0x27:
Power Supply
A redundant power supply has failed inside the tape drive
enclosure. Check the enclosure users manual for instructions on
replacing the failed power supply. 

Freeze media 1159L4

# bpmedia -freeze -m 1159L4

You can use the GUI under media management as well

Call vendor and let them have a look at index 0, that tape drive is the culprit in all 3 errors. Those 3 errors are hardware errors as Marianne pointed out.