Error:

The writer vetoed the shadow copy creation process during the
backup preparation state. (VSS_WS_FAILED_AT_PREPARE_BACKUP)

Cause:

This typically happens with Exchange 2010 when CyberSecure signals exchange to create a VSS snapshot and the shadow snapshot fails to be created.

The reason for this is one of two things:

1. The Exchange VSS writer is in an unstable state
2. Some other backup software also has an exchange volume shadow copy created at the same time as CyberSecure

Resolution:

1. Check the state of the VSS writers on the system by issuing the following command as an administrator user in a cmd.exe shell:
   1. vssadmin list writers
      Here is an example of the Exchange VSS writer being in an unstable state:

      Writer name: ‘Microsoft Exchange Writer’
      Writer Id: {76fe1ac4-15f7-4bcd-987e-8e1acb462fb7}
      Writer Instance Id: {7a58fc86-40db-4464-88c8-d6e8fc2eea90}
      State: [7] Failed
      Last error: Retryable error 

      The correct state of the VSS writer should be:
      
      Writer name: ‘Microsoft Exchange Writer’
      Writer Id: {76fe1ac4-15f7-4bcd-987e-8e1acb462fb7}
      Writer Instance Id: {7a58fc86-40db-4464-88c8-d6e8fc2eea90}
      State: [1] Stable
      Last error: No error

   2. If the writer is showing a failed state, then restart the “Microsoft Information Store” service and check again.
   3. Should the writer often be going into an unstable state, it may be a sign of underlying problems with your environment.
2. Disable or uninstall any other backup software that is running.
   If this resolves the issue, then try scheduling backups at a non conflicting time.