How do you trigger the btn inside a movie clip

1

I have a box_mc on the stage and I create a btn inside the box_mc.

the code in the class:

========================

btn.addEventListener (MouseEvent.MOUSE_DOWN, handleMouseDown)

function handleMouseDown ($evt:MouseEvent):void
{
do something();
}

=======================
Also try:

box_mc.btn.addEventListener (MouseEvent.MOUSE_DOWN, handleMouseDown)

function handleMouseDown ($evt:MouseEvent):void
{
do something();
}

========================
Error: 1120: Access of undefined property btn.

NOT WORKING… I AM MISSING SOMETHING??

Thanks.

NB