screensaver problem

I just got a new macbook pro, but some of the new screensavers I've downloaded won't work. It gives me a message saying "can't load screen saver. You cannot use the screen saver (whichever screensaver it is) on this computer. Contact the developer of this software for a newer version." However, I know it's installed correctly because the screensavers work on my backlight 2 program. I just can't change the settings for them. Can anyone tell me what's goin on?