This article explains troubleshooting steps to resolve the agentless backup error message "Critical Backup Failure: ServerFaultCode: A specified parameter was not correct."
This error message can be caused by an issue with the changed block tracker issue on the protected machine.
To resolve this issue, reset the changed block tracker on the protected machine by either:
- Resetting the CBT on the host as described in the VMware article Resetting Changed Block Tracking for VMware vSphere virtual machines; or
- Destroying the agent's live dataset and running a new full backup.