We are running VDP 5.8 on vSphere 5.5. One of the appliances failed to backup a VM last night. Checking the VM in the client, there is a message to consolidate the disks. I attempt to consolidate by right-clicking on the VM > Snapshot > Consolidate and it failed with this error:
locked

I checked the vmware.log file for the VM and saw this error:
2015-09-15T03:00:29.146Z| vcpu-0| I120: DISK: Failed to open disk for consolidate '/vmfs/volumes/5490a09a-eb6682ee-affb-bc305bef5520/mobxxxxxx/mobxxxxxx-000002.vmdk' : Failed to lock the file (16392) 8162

I check the settings on the VDP appliance and notice that the VMDK that belongs to the vm is attached.

extra-vdp-disk

Shut down the VDP appliance and remove the disk. Making sure to only remove from virtual machine and NOT remove from virtual machine and delete files from disk.

remove-extra-vdp-disk

Run the consolidation and if it succeeds, re-run the VDP backup on out of date sources to remediate your failed backup.