Is LR closed when you are trying to delete the Lock file?
Close LR if it is running.
Using Finder or Explorer, verify that you have READ and WRITE access to everything in the folder containing your catalog.
The catalog is located on an external hard drive and when I click "get info" on the drive is shows that open to read and write. Should I be looking somewhere else?
Please restart your machine and then try to delete the lock file.
had the same problem and finally uninstalled & reinstalled lightroom..
the .lock file aswell as the catalog-journal file disappeared.
Check the "get info" in the drive and the folder and the actual files.
That's great..!! thanks for trying.