NBU status: 2074, EMM status: Disk volume is down

Thanks for your reply David.

There was no disk pool down and i cross checked it. I found in a tech note that any backup job to DataDomain fails with error 2074 - Disk volume is down when there are already active jobs writing to the same volume. I was getting the error until multiple jobs were running but when there was only one job running, I ran the command nbdelete -allvolumes –force on master server which executed successfully. After that I ran bpimage -cleanup –allclients and this time the image cleanup command ran completely successful. So finally issue got resolved.