The maximum of 256 initiator sessions per initiator node were established from one or more target controllers. Each invocation of the addiscsistorageport command creates an additional session through the nodes in the specified I/O group or cluster.
Use the management GUI or the lsiscsistorageport command to check the total number of sessions per node. Use the management GUI or the rmiscsistorageport command to remove any sessions that are no longer in use. When the number of sessions is below the maximum, try again to establish the session.