Netbackup SAN MEDIA Server to back up exchange multiple passive node fail

Hi,

I have a Exchange 2010 DAG with 3 node, 1 active and 2 passive. Each of the exchange server is a NBU 7.1 SAN Media Server, in which in a normal backup, it can backup only it's own data. I wish to backup the passive node onto a tape library

However, wheneven a backup job for the Exchange DAG is being done, the 2nd passive node always fail with errors pertaining to communication betweeen server.

Does SAN MEDIA Server cannot be use on a passive backup of a 3 node exchange DAG?

Thanks