You should also understand, Frameskip and Fast Forward, are two distinctly different functions.
Frameskipping should be left alone, and on the setting where your PC plays the game best at as close to original speed as possible.
As already reccomended you should probably unzip to a fresh directory, if you've by chance made a habbit of simply overwriting files. Backspace works for me in Fusion 3.5
But if it really bugs you and you can't fix it for some reason, you can always turn it on and off via the Video drop-down menu.