Cannot call _root movie clip from a child movieClip

programming flash
1

Hi this is the scenario:

I have two scenes : Menu,Game

A movieClip: MenuScreen ( called through attachChild )

A button : Start Game ( Inside menuScreen )

The button StartGame calls a function on the root to play the next scene. This situation works fine, but if I try to use menuScreen (movieClip) somewhere else ( create an instance ) the first StartButton stops working.

Any Ideas?

FahimAkhter