NDMP Error - hmmmm

We've recently upgraded to BE2014. Some of our jobs are immediately failing whilst 4 are running with the following error:

NDMP Log Message: DUMP: Maximum number of allowed dumps/restores (4) in progress.
NDMP Log Message: NDMP_OP_ERRORCODE is 'EMAXBACKUPS'
NDMP Log Message: DUMP: Dump failed to initialize.
NDMP Log Message: DUMP: DUMP IS ABORTED
NDMP Log Message: DATA: Operation terminated: EVENT: INTERNAL ERROR (for /vol/EXMBX_DB_05)
NDMP Data Halted: Internal Error
NDMP Mover Halted: Connect Closed

Any ideas what is going on? 

We have 7 drives across 2 libraries backing up from multiple NetApp controllers that are running Ontap 8.2.2

The strange part is that 5 backups had started fine. One job completed and the the next scheduled job failed with the above error within seconds, the next one after started and failed within seconds, the third and fourth the same and then the fifth one starts fine......

I'd be grateful for your help.