SCSI tape drive cluster troubleshooting assistance

4 tape drives:  Fileserver, Exchange, Tandberg, LTO2 (don't ask about the names...)
Using Symantec Backup Exec 15 version 14.2 (I know we're behind, discussing a new solution in 2017)
"Inventoried" all 4 tape drives
Attempted to backup "Intranet"(smallest backup job we have, ~250MB) to "Exchange" -- failed with physical device error
Removed all tape drives EXCEPT fileserver.  Plugged directly into Fileserver tape drive with terminator, succeeded.
Plugged into Exchange, succeeded.
Plugged into Tandberg, succeeded.
Plugged into LTO2, succeeded.
Connected FileServer + Exchange - Succeeded
Connected FileServer + Exchange + Tandberg - succeeded
Connected all 4 - failed
Connected FileServer + Exchange + Tandberg = succeeded
Cluster is in order as follows:  1. Fileserver 2. Exchange 3. Tandberg 4. LTO2

Why would I back up just fine to LTO2 while directly connected, but once I add it to the chain/cluster, my job fails.  On the individual tape drive tests I was plugged directly into that tape drive and the backup job was pointed at each tape drive I was plugged into.  Once I added more than 1 tape drive I was backing it up to "Exchange" as that's the designated destination for the backup.  As I state, with 2 tape drives it works, with 3, it works, add the 4th and it fails.