I also had problem with locked file.
ESX is a single host, local datastore, the VM has 4 manual snapshot, no space problem on datastore, need consolidation=true.
The backup software VM started backup, I received alarm, went on vsphere console and found VM was suddenly switched off.
The backup failed (also all 4 retry), inside the vm folder new delta file were present but no snapshot point (not present in vmsd file).
The file locked is the last delta vmdk from manual snapshot, in exclusive mode, from the local esx.
No process are using this file, file is not mounted in any other VM.
Cannot copy or delete the file, can rename it.
Tried consolidation, failed with locked problem.
Did new snapshot and deleted all the old snapshot without error, but the process was too fast, in fact all delta files still there, but not anymore in the snapshot database.
Tried new consolidation and failed with error "file not found".
I will reboot host ASAP but it seems strange that if no one is using the file it still locked. In any case it seems I need to manually rebuild the chain of snapshot.