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BugZero found this defect 4665 days ago.
A Backup or Replication tasks fails with the following errors: "VSSControl: Failed to prepare guest for freeze, wait timeout 900 sec." "VSSControl: Failed to freeze guest, wait timeout"
Possible Security Software Interference Anti-virus software may impede VSS operations. As an isolation step, consider temporarily uninstalling the Anti-Virus, rebooting, and rerunning the Veeam job. A complete uninstall is necessary as simply disabling some anti-virus solutions may still leave components active. (AV Exclusions)
Both errors are related to Application Aware Image Processing. As a temporary workaround, you can disable AAIP in order to obtain crash-consistent backups. For more information, consult the user guide overview of Transaction Consistency.Overview of Processing a Backup Under VSS has a visual explanation of the freeze timeout (the green box).