Deactivate licence error

I have an existing free licence since 2019. I have just bought a Personal Licence because I want to add a third email account on my desktop PC. I am running the latest version 10. When I try to deactivate my free licence, another window pops up asking me if I am sure I want to. I click on “yes” and eM Client instantly stops running altogether. An error message appears asking me what I was doing. If I complete the box and ‘continue’, eM Client comes back - but the same thing happens again when I try to activate my new licence again.
The deactivate window is not changing as it should to a new activate window for me to enter my licence key. this is very frustrating. Please advise what to do ASAP. Thank you.