The lock file is going to be regenerated every time you open Lightroom. However, when LrC closes properly that file will automatically be deleted. It has to be there because it's part of the database engine that drives the catalog. Are you saying that you still cannot open Lightroom Classic?
Whenever LrC starts normally a lock file is generated. It has to be there, you must not delete it. Leave it alone! It is a file that you should ignore. When Lightroom closes normally LrC will delete it automatically, and you won't get any of those "other application" notices. Don't look for that file, it isn't anything that you should even be aware of under normal circumstances. The only time it should become a concern is "IF" Lightroom shuts down abnormally and that file gets left behind. It is then that you have to go in and find it and delete it. Otherwise, it is a file that you simply ignore.
The fact that i had to use a thread from 2008 to solve an issue in 2020 is all kinds of wrong.
Although your search for an answer took you back to a 2008 conversation doesn't mean there aren't newer posts/replies that deal with the same problem. A Lock file was left behind in the folder the catalog is stored in because of either a LrC or system crash of some kind.
A Google search for Lightrrom classic won't start because the catalog is being used by another program give you this.
My point was that we're twelve years on and this is still an issue.
Adobe cannot absolutely guarantee that Lightroom won't crash on YOUR computer at some point. Lightroom could shut down Abnormally for any number of reasons, and IF that happens the lock file would will be left behind. It's part of the database engine that makes the Lightroom catalog function. It's my understanding that there is a function built in to Lightroom to search for orphaned lock files to delete them, but I'm not sure when that function was introduced. I don't know what version you are using, but it's possible that the function isn't there or that the lock file was simply overlooked this time. Computers are not infallible.
I see my duplicated file but when I click on it it will not delete and I can't open file or edit when this screen is open. Any ideas? Thanks!
I have no idea about a "duplicated file" (not the theme of this long thread!)
You best start a new post thread, and- Include the following in your question:
Adobe product and Version number
Operating system and Version number
The full text of any Error Message(s)
What you were doing when the problem occurred
Screenshots of the problem
A Screenshot of the info panel from MENU: Help/System Info...
That sorted it for me too. I am running the latest version and windows 10