The VCenter server got corrupt and needed to be restored and errors out with the "An internal error occurred during execution, please contact Quest support if the error persists. Error Message: VMhost06.domain.com is being managed by a Virtual Center. Please disassociate the host from the Virtual Center before continuing a Restore operation or register the Virtual Center in vRanger."
When the VCenter server went down the ESXi hosts still think they are being managed by VCenter. Using the VSphere client, logging in as root you get a message saying the host is being managed by VCenter. This is caused by the VCenter agent still running on the hosts.
The host you are restoring the VCenter VM back to, you will need to restart the management service to stop the VCenter agent. (*** Note... Make sure Virtual Machine startup and shutdown are set to disabled (In vSphere->Click on the host-> Configuration-> Security Profile) If enabled the VMs on that host will reboot. ***)