Targeting Button Inside loaded MovieClip

Hey there,

I think I am loosing it ...

Anyways, I have loaded a Movieclip onto the stage with:

_root.attachMovie("MCCheck","MCCheck",(1001)); // Attaches the Check Button
_root.MCCheck._x = 82;
_root.MCCheck._y = 202;

and would like to target the button (instace nameis butCheck) inside movieclip or just use a onRelease command to do something. I thought the code would go:

_root.MCCheck.btCheck.onRelease = function() {
trace("go");
gotoAndPlay(1);
//play();
}

But I am wrong.... and suggestion wher I went wrong