VTL Drive going down and Job manager lost message channel unexpectedly error. (4047634)

Date: Feb 11
Product & Version: NetVault All
OS Version: All
Module & Version: N/A
Application version: N/A

Symptoms:
-A lot of backups are being performed (Full, Incremental and Consolidations).
-NetVault environment setup:
 

NetVault Server and Clients on site A and all connected to a Multi Mode Cisco MDF-9124 FC Switch.
Then a single FC connection from site A to site B to another Multi Mode Cisco MDF-9124 FC Switch, where the Quantum DVi7500 is connected to.
Backups on the Client are setup to “Local Drives Only” on the Target tab, so that backups are performed over FC.

-Small backups work OK, but the errors only happen on large backups above 200GB.
-FC Switch on Site A has many of the following errors and that is why the connection to the VTL goes down i.e. bottleneck:

FC switch error. MAC bit error exceeding threshold. Bit error rate too high.

-The many errors we can see from the Binary Log are:

1] Error 2011/01/22 07:07:52 0 Media backup Command failed, re-initializing driver
With sub text:
SCSI 14 0 70652 CMD PREVENT/ALLOW MEDIA REMOVAL [ 1e 00 00 00 00 00 ]
CAMDARWN 3 0 70652 ScsiCamCmd (BEGIN)
CAMDARWN 4 0 70652 Got SCSITask object
CAMDARWN 64 0 70652 COMMAND HAS NO DATA XFER
CAMDARWN 6 0 70652 Set scatter-gather list
CAMDARWN 7 0 70752 Sent command OK - status (4)
CAMDARWN 8 0 70752 Got SCSI Service response (1)
CAMDARWN 10 0 70752 Task did not complete
CAMDARWN 16 0 70752 ScsiCamCmd (END)
SCSI 15 0 70752 CMD failed: errno 0

2] Error 2011/01/22 07:07:52 920 Media backup 'backup: FIBRE-WWN-50 0e 09 e2 00 33 c0 00 -0 (QUANTUM DXi7500): DRIVE 10:backup' has gone down
3] Error 2011/01/22