Sysvol free space
Maybe a snapshot has not been removed and the diff disk has grown over time.
Please proceed as follows to remove all snapshots generated by NovaBackup DC and thus clear the sysvol.
Open a cmd.exe as admin and change to the directory
C: \ program files \ novastor \ datacenter \ hiback \ vss
Run the command there
vssdba.exe -delete *
off if no backup is currently active on the system.