Symptoms:
To resolve this issue, remove the virtual machine disks from backup proxy virtual machine.
For more information, see Consolidate Snapshots and How do I Add a Hard Disk to a Virtual Machine.
Note: The backup proxy VM is one or more of the backup application virtual machines. If you have multiple backup proxy virtual machines, it is necessary to check all the virtual machines as the disk (.vmdk file) in question may be attached to any of them.
Refer Kb to identify file lock: VMware virtual machine file lock on VMFS datastore