What happens when you run
I have been using Backuppc for a few years now. Recently I upgraded my machine to newer, faster hardware. Hence, I have experience exchanging ssh keys, etc.
It seems I have one client that refuses to connect via ssh. When I exchanged keys and ran "ssh -l root [clientip] whoami" the client properly returns 'root'. When I "sudo -u backuppc /usr/share/backuppc/BackupPC_dump -v -f [clienthostname]" I get 'dump failed: Unable to read 4 bytes'.