There are some issues around celerra iscsi snaps and RM. It might be a situation where orphan snaps exist due to a timing issue when deleting and creating new snapshots. There are some workarounds and fixes around this are. I suggest you open a ticket with support and provide RM debug logs. Orphan snaps will need to be checked and removed by support. Take a look at emc149820 also or quote that when opening a ticket.

Regards,
Alan