iscsi replication

I am trying to setup an iscsi replication session between a Celerra ns500 and an ns40. we already have cifs file systems replication so there is a trust between the two cabinets. I have replication manager and have installed the server on one host, and agents on two other hosts. My understanding being that i could manage the replication from the RM server host with the others being a production and a mount host. I have setup the destination lun on the ns40. The production host can see an iscsi lun on the ns500. I am trying to replicate the ns500 iscsi lun to the ns40 iscsi lun. However, when I setup the job in RM, it says it cannot find an available license for the ns500 host. What license is it referring to?