yes you must uninstall. that way you get a clean reinstall. Also what os you running? win 98 or XP. If XP you need to shut down all programs that boot up. how? by task manager ->processes->end task all programs that have your user name next to it. This would apply in win2k too. Please read the uininstall messages carefully. I did not have to re register the software as everything reinstalled cleanly and all worked and was accounted for. Hopefully this does the trick for you.

I have XP and it is best to let the machine completely shut down before switching it off (everyday practise). I had to rush out one day and switched the machine off prematurely which curropted the .ini file. I wasnt even using real flight that day

Good luck