The fact that it was necessary to restart the server to get it working again points to a bus level problem that resulted in a loss of communication to the tape device.
Typically a SCSI reset is sent to re-establish communication but it seems not in this case.
Still a lot of things can cause SCSI errors.
Check Event Viewer System log for errors from the controller at that point in time.
Configure HP Management Agents not to collect SCSI Information.
Update the
controller firmware and driver.
Try a new controller, cable, and terminator.
If there are any other devices on the bus move them to a different controller.
If the controller driver is Storport then they library and drive have to stay enabled, but if the SCSI Mini port controller driver is used, then disable the library and tape drive from within the OS Device Manager.
