The screensaver MIGHT not work because you downloaded but might not have installed it. Double click on the icon that is probably on your desktop. You will then probably see some icons in there, one being the install icon. Double click on that and follow the directions.
I am only writing this because I downloaded a Cinderella screensaver 3 times until I figured this out. Everytime I tried to use it, it gave me an error box. UNTIL, I did what I wrote above.
This might not be your situation, but thought I would try and throw it in for good measure. If it works, which I hope it will, then that's great!