We have the same problem. In our case, I believe the problem was a result of an upgrade from VSC 2.x to VSC 4.1. We are seeing the exact same thing as smora_netapp and Tatsurou Ide. Same exact thing. Any one had any luck in resolving this?
You can't really tell a lot from that 1 line. Usually arond that line I'm used to seeing 'cant find xxxx as a vm, can't find xxxx as a datastore, can't find xxx as a ....", which usually means something like an object was deleted from vCenter but is still part of the backup job or something of that nature.