I know this is a really old thread but I ran into this on ESXi 5.1 while converting an old 2003 server. The network connection was lost to the machine being converted. rebooting is a last resort for me but i just ran services.sh restart from the host that had the lock. I found the lock using the above command, however i added a grep to it because it was just to much stuff.
lsof disk1-name.vmdk |grep disk1