You must close LightBurn before you delete the prefs file as it is re-written each time you close the application.
Are you saying you get a message when you run LightBurn? How can this be if you deleted LightBurn? Are you saying if you try to re-install after you have deleted LightBurn you are getting this message? Or 3rd, are you saying that if you try to say that when you try to activate your license, you get a message telling you that you have reached the license limit?
We are trying to help you resolve your issue and are not trying to be difficult. You are not helping this along though. We respond to you and also ask you questions that you do not answer, making this harder to track down what the issue is and how best to help resolve.
If English is not your first language, please try posting in your native language. That might help and we can do the translation on our end.