[Lizard]

This .lock file is used to indicate that OmniFocus is using your file, so two different copies of OmniFocus don't try to edit it at the same time and confuse each other. So either OmniFocus somewhere else is using the file, or OmniFocus crashed the last time you used it and didn't get a chance to clean up after itself, or something like that.

1) Double-check that there isn't another copy of OmniFocus already running in your dock.
2) Go find and delete that lock file. It should be in the same folder as your database. By default this is in [user name]/Library/Application Support/OmniFocus, but you might have moved it somewhere else. From the error message, it sounds like it might be in "Wombat HD".
3) Now you should be able to open your database again.
4) If you do have your Focus database on a removable hard drive, always be sure to quit OmniFocus before you eject the hard drive.

If you continue to have this problem, I suggest you email our ninjas (omnifocus@omnigroup.com) so they can help figure out what's causing it.