Unable to do back ups,"Device cannot respond"

[guest]

SOLUTION/WORKAROUND:
-but the medium changer was not detected in the device manager.
-changed the library mode to random still it did not get detected.
-requested the customer to connect the RTL using the same scsi card.
-now the medium changer gets detected in the RTL.
-but the driver was not symantec.
-installed the symantec driver and restarted the server.
-ran the backup job and issue resolved.
-assistance on changing the library mode is on a new ticket with customer's permission.