Customer had the following netbackup setup:
two classes
different volume pools specified for each class
same client in each class
one filesystem in each class
MPX disabled
ETL 7/3500 with 5 drives


Customer tried to kick off a manual backup for both classes at the same time 
and one goes into an active state and the other stays queued until the first 
is done. Customer wants both to go active and write to two different drives.      

In the netbackup administration gui (xbpadm) under file-> change netbackup configuration
change the Maxium Jobs Per Client to be greater than 1 ( which is default), in this case 
setting it to two will allow the client to run two jobs at a time.