Backup fails do to: “VZ Mutex lock failed()” Error. This error occurs only time to time and not on the same VM’s
If you receive occasional .vzmutex but it is not consistent that means that your ESX host might be very busy to accept new backup connections.
Occasional .vzmutex but not consistent errors. - Your ESX host might be very busy to accept new backup connections.
Please check your configuration and make sure that is set to default. (Default values are found on Page 18 in vRanger 5.0 Evaluation Guide)
If it is not you might be over taxing your ESX hosts.
vRanger Evaluation Guide is attached to this KB
Also please lok at performance tuning recommendations of VMware ESX Service Console: