After a few replica’s on SharePoint 2013, DPM backups kept failing with the above error. If you run a consistency check then all is good until the next backup.
To fix this error you need to increase the USN Journal, you can do so as follows, run the following PowerShell Command (increase to whatever suits your environment):
fsutil usn createjournal m=1000 a=100 c:
After running this command I was able to create a replica again, here is the MS Technet Article:
Hope it helps