NetVault Device Manager doesn't recognise a tape library changer, but drives are visible.
Drives also visible in Windows Device Manager, but not the tape library changer.
In order for NetVault to see a device, then the Operating System has to see the device as well.
Installed HP Tools, rebooted NetVault Server and can now see the changer in the Operating System Device Manager.
Could then install the tape library into NetVault Device Management.
Note: You should not install any device Drivers, as NetVault has its own Device Templates that communicate with the device over the SCSI Protocol communication channel.
The only time that you can install Drivers, if the Operating System cannot see the device in Windows Device Manager.