When I try to quit from the Results screen using the control at the top of the window (red X for Windows XP and OS X, tiny square for OS 9), the program hangs. How can I avoid this problem?

Update your software to version 2.0.3. In Read Naturally SE 2.0.3, when you quit from the Results screen you will automatically be returned to the Congratulations screen and you can exit the program from this screen. Download the SE 2.0.3 update.