Did you try knowledgebase search on the Symantec support web page?
http://www.symantec.com/business/support/overview.jsp?pid=15143
NBU5.1 does not have EMM, it will not activate/deactivate the robots and tape drives individually ... strange.
Try robtest, check if you can see the robot path from the OS (cat /proc/scsi/scsi) and do scan (/usr/openv/volmgr/bin/scan)
What's the exact message syntax in syslog ... any other messages in there?
Also, try stop NBU services, make sure everything's gone (bpps -a) and start vmd (/usr/openv/volmgr/bin/vmctrldbm -i) and start ltid (/usr/openv/volmgr/bin/ltid -v) and check out the syslog again.
Abe