These are external SCSI messages relayed to NVBU i.e. is an issue outside of NVBU and advise to contact your hardware vendor to test everything from the NetVault Server to the Filer and to the tape library (FC Cards, FC cables, FC Switches, HBA firmware, tape library, drives, tape library firmware, drive firmware, Filer and motherboards where the FC cards are inserted to. The same applies to SCSI connectivity).
If anything is replaced, upgraded or re-attached, then you always have to remove the tape library within NetVault Device Management, reboot the NetVault Server, re-add the tape library within NetVault Device Management so that a new NDMP channel to the tape library is created.
Note: The tape library engineer needs to perform tests from the NetVault Server and not just plugging in a laptop into the tape library, as all the communication from the NetVault Server to the tape library and everything in between needs to be tested.