When backing up a number of Virtual Machines or a Backup Group the majority will be successful but a number of VMs may fail randomly with:
"Error Message: Cannot backup vm 'VM_NAME'- snapshot hardware configuration mismatch. Please commit all open snapshots before continuing backup."
The cause of this may be contention on the host or LUN.
In vRanger, navigate to Tools | Options | My Jobs | Configuration
In the Resource Management Panel, lower the values for:
Maximum number of tasks running off a LUN & Maximum number of tasks running on a Host