Cannot Deactivate Lightroom 6 as it won' t start

I am using Lightroom 6 and receiving the following error ?:0: attempt to compare nill with string

and it will not open. I have tried multiple catalogs and it seems to want to open and then fizzles out and shows me that error.

Adobe will not assist me in deactivation quoting end of life product and no support.

So, I need to know that if I uninstall it on that  computer and then reinstall it,  will Lightroom open since I cannot currently open it  and deactivate, I am concerned it may think this is a third activation and over the limit.   

If this doesn't work does anyone have any workarounds.

Not interested in subscription service. Thanks

?:0: attempt to compare nill with string

This error message has been mentioned many times in the forum, and solutions are available, but I don't know what the solution is. Please search the forum.

Sounds like your catalog may be corrupted, but first check your catalog folder for a file that ends with '.lock'. If that file is present, then delete it and start Lightroom. Does that solve the problem?

If that didn't solve the problem, then try if replacing your catalog file with a backup solves it.