This happened to me right after installation (with no restart), but after I restarted the computer it was fine. I also reinstalled FSUIPC (registered) just for the hell of it as I have the current version backed up in a safe place. I recommend that as it will automatically re register itself and all your previous FSUIPC settings should be there. Always restart your PC after installing an FS add on, it eliminates alot of problems that really wouldnt be an issue if you did.