ActionScript 3.0 :: Getting An Error #1010?

I originally had a button named hairOne for a dressup game, I later swapped a symbol with another symbol, gave it the correct instance name, but now I keep getting error #1010 "a term is undefined and has no properties". yet if I go back to the old symbol it works, why wont it work when I swap the symbol with another is what I can't figure outso heres what it sort of looks likeheres an instance name of a button = haircolourand heres the codesum public function {

haircolour.addEventListener(MouseEvent.CLICK, oneyesButtonClick);
}
another public function oneyesButtonClick(dostuff:yeah):void {

[code].....