Unable to delete a flat-vmdk file from VMFS5 volume
Start by identifying the server whose VMkernel may be locking the file.
# vmkfstools -D /vmfs/volumes/UUID/VMDIR/LOCKEDFILE.xxx
 > Hostname vmkernel: gen 532, mode 1, owner xxxxxxxx-xxxxxxxx-xxxx- zzzzzzzzzzzz mtime xxxxxxxxxx]
zzzzzzzzzzzz gives the MAC adres of the server locking the file.
# lsof | grep -i LOCKEDFILE.xxx
OR
# vmkvsitools lsof | grep LOCKEDFILE.xxx
You see output similar to:
11773 vmx 12 46 /vmfs/volumes/Datastore_Name/VirtualMachineName/ VirtualMachineName-flat.vmdk
kill -9 PID (in the above case 11773)