Extract from binary log:
Error 2015/09/17 20:44:06 67 Data Plugin NETVAULT Replication failed 'Plug-in, server version mis-match'
Job Message 2015/09/17 20:44:06 67 Media NETVAULT Device 'DR4x00 (BAtoBH) - 192.168.152.231' has completed its transfer
Warning 2015/09/17 20:44:06 67 Data Plugin NETVAULT Replication method for stream cannot be used, falling back to standard stream copy method
Checked DR4100 software version and one was using software version 3.1 and the other was using software version 3.2
DR4100 software version mis-match
Upgrade the DR4100 running software version 3.1 to 3.2