Scroll Wheel Triggering Expose

I have had my mac set up for accessing dashboard using F13 and my mouse's scroll wheel to trigger Expose's All Windows for years now. Out of nowhere my settings changed (only thing new to my my machine is World of Warcraft, which maybe caused the change?) getting the Dashboard back to F13 was no problem however...I have been unsuccessful at getting my mouse set back up so that the scroll wheel triggers "All Windows." I am using an older Microsoft wireless optical blue mouse, I know the mouse is able to do it because it has worked for years, I have also been to system preferences,mouse and keyboard but when i choose mouse there is no option to assign the scroll wheel. Anyone have any suggestions?

Go to Dashboard&Expose settings in Sys Prefs. Look down the lower RH side and see if any mouse settings there have been set or changed. For example, I have no mouse shortcuts whatsoever, preferring to use the keyboard only.

Try what Hugh suggested. Also were you using a driver for the Microsoft Mouse at all or just stock OSX? Reason I ask is there is a driver that Microsoft provides for some of their mice for OSX.