Just wanted to say that i got an adwise in the thread that i posted earlier that has worked for me.
Adwise form Softwater:
Try deleting this file:
~/Library/Preferences/com.apple.screensaver.plist
and then re-starting your mac.
Don’t worry, deleting the file is harmless. It will just recreate itself to default settings when the computer reboots. It may be that the current file is corrupt.
Note: to get to this file in Lion, you have to chose ‘Go’ menu from the Finder menubar at the top of the screen, while keeping the ‘option’ key held down. When you do this, you will see ‘Library’ in the Go menu bar. Click on it and navigate to Preferences and look for the filecom.apple.screensaver.plist and trash it.