NovaBACKUP PC/Server/BE v19.x and newer
In the Windows Event Viewer "Application" you will find error messages regarding the ASR Writer. The backups fail or you find warnings in the backup logs.
With the command "vssadmin list writers" you can check the status of the VSS Writer. If one of the writers is in an error status, you must determine the cause. Often a reboot fixes the problem. If it occurs again, check the system for malfunctions (defective hard disk, missing disk space, hard disk/partitions offline). The Windows Event Viewer is a good first port of call here, check Windows event log "Application" and "System".
If the ASR Writer reports problems, this is sometimes related to the hidden Windows boot/system partition. Assign a drive letter for this hidden partition once via the Windows Disk Manager and restart the backup job.
Also please read this Microsoft forum post:
More details regarding ASR Writer: