VSS snapshot errors/warnings
If you seem to be getting logs of VSS-related errors and warnings for image or File-by-file w/ Locked File Agent backups, try the following to check the status of your VSS Writers:
Get to a command prompt, and type: "VSSAdmin list writers"
This command will instruct Windows to query the current status of all the VSS writers on the system. This can help you find out if one of the writers has an issue that could be causing failures to freeze drives.
Technical Support Manager