I'm getting this error most of the time but sometimes, the same backup job is successful also even without doing anything. Running on Windows 2012 R2
V-79-57344-34108 - An unexpected error occurred when cleaning up snapshot volumes. Confirm that all snapped volumes are correctly resynchronized with the original volumes.
Go to the VM and see whether you can manually create and delete snapshots. Make sure that you have sufficient space on your disk for snapshots.
Also, see this document
http://www.veritas.com/docs/000007156
Assuming this is traditional agent backup and not a VM backup check the Windows Event logs inside the server being backed up for VSS errors at the time of the backup - if there are any research those errors
