Have you checked the DD Plugin version on both NBU servers ( Source and target ) ? I had a same issue where the DD plugin version wa lower the 2.6 on target NBU server.
Boomchi
As asked by Marrianne please send the output of nbemmcmd -listmedia -mediaid <media-id> and follow the instruction of Marrianne and Mark ,
if still the issue is not fixed then It may be an issue with the nbrb allocation , I have noticed it many times...