Ok, I have Windows Vista and this is the first time I've noticed this happen. When I right click the desktop and it takes me to appearence and personalization, it'll have a list of things I can click on, which are:
Window Color and Appearence
Desktop Background
Screen Saver
Sounds
Mouse Pointers
Theme
Display Settings

Everytime I click on one of these (except for Desktop Background, an error message will come up saying "Windows cannot find 'C:\Windows\System32\rundll32.exe'. Make sure you typed the name correctly, and then try again."

How do I fix this? I'm not typing in anything, just clicking. Thanks in advance.