I am posting this here because the subject describes the problem I encountered as well. Though, it may be different because the solution provided did not help me.
Recently I lost the function of F6-F12 keys on my aluminum keyboard.
After trying the above solution and not finding the mentioned plist file, I played around with my Keyboard preference pane and fixed it for myself. At least for now.
In the Keyboard pref pane > keyboard tab, I checked the box "Use all F1, F2, etc. keys as standard function keys". I switched to another pref pane and then back. I then unchecked the same box. Now all the keys work properly.
What caught my eye in the first place was that the keys would work how "I desired them to" when pressing the "fn" modifier. I then realized that the computer was acting as if that "Use all F1, …" option was selected.
Message was edited by: DLR