Removable Storage (RSM) should not be running when Backup Exec is on the system, it can cause conflicts. RSM will try to take control of the library, so BE and RSM will fight over the device and cause problems for the system.
You can also use our tracer program (technote below) to monitor what is getting sent back and forth to the library. This is a good way of checking for any problems. The library may be fine, but the SCSI card could be going out. tracer can help to determine where the problem is.
Also, check your event logs. If you see any event ID 5, 7, 9, 11, or 15's coming from either your SCSI card or the library then you really should get in touch with your vendor to have them look at the device.
As for the unknown media changer for the library, this is what it should be set to. BE only has drivers for the tape drives, not the changer.
Tracer Technote - http://seer.entsupport.symantec.com/docs/285630.htm
General Hardware troubleshooting technote - http://seer.support.veritas.com/docs/255501.htm