Calling Global Function from embedded movie clip

Hi Guys,
I have what i hope is a pretty simple question. I have a standard “ButtonClass” global function which is use for all buttons. Its a rollover function that fades in an out on rollover and rollout. However, when i try to call this function from a button embeded within another button, the function no longer works. Can anyone point me in the direction of a global function which works on an embedded movie clip for something as simple as rollover actions?