Backups failing - freeze/thaw VSS failures or broken Agent when Antivirus is used


Security software known for either damaging


Backups fail citing VSS freeze/thaw events and customer is utilizing an Antivirus.

GetWriterStatus: USNAPError! GatherWriterStatus call has returned a failure.
(VSS_E_WRITERERROR_TIMEOUT) The writer's timeout expired between the Freeze and Thaw events.
Please check Windows Events Log that Volume Shadow Copy Service and VSS Writers are operating properly.

To confirm, leverage the command:
# fltmc instances


Sophos Antivirus has provided their own KB in regards to how to prevent this issue in their software. Please see the following KB written specifically to address this ongoing issue:

In addition to the above Sophos fix also confirm that the exceptions listed in this KB 5800 are applied for your antivirus programs. For any other Antivirus program, if you need assistance with making sure the appropriate exclusions are made to prevent scanning Windows Shadow Copy volumes/location, please contact your Antivirus Software support team.


Antiviruses with Real Time Protection and/or Intrusion prevention Services may have unexpected impacts to the success of guest-level backups.


For details on the 'fltmc instances' command see

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