Try the steps below
1. Create a new backup selection or if possible the whole job.
2. Do not select C:\SYSVOL in the backup selection as this is by default backed up from the System State of that Server. And this error might be displayed due to the fact that the default internal exclusion for the SYSVOL directory was not properly formatted
3. On the Advanced Open file tab in the backup job select to use AOFO
4. Select use Microsoft Volume Shadow Copy Service in open file configuration
5. For Snapshot provider use “System – Use Microsoft Shadow Copy Provider”
6. Make sure that the Process Logical Volumes for backup one at a time is checked.