Load .swf && sliding menu

Below is the code from a siding menu that works fine…

[AS]onClipEvent (load) {
xcenter = _root.box._x + ( _root.box._width/2);
speed = .03;

lowX = _root.box._x;;
highX = lowX - (this._width - _root.box._width);}

//**************************************************
onClipEvent (enterFrame) {

if (_root.box.hitTest(_root._xmouse, _root._ymouse, false)) {

var distance = _root._xmouse - xcenter;
_x -= ( distance*speed );


if (this._x >= lowX) {
	this._x = lowX;} 
else if (this._x<=highX) {
	this._x = highX;}

}
}
//**************************************************[/AS]

However after loading this into another movie it wouldn’t move, I made some changes and now it scrolls only to the left. Can someone please tell me what I have over looked ???

[AS]
//**************************************************
onClipEvent (load) {
xcenter = _level0.tops_contain.box._x + ( _level0.tops_contain.box._width/2);
speed = .03;

lowX = _level0.tops_contain.box._x;;
highX = lowX - (this._width - _level0.tops_contain.box._width);}

//**************************************************
onClipEvent (enterFrame) {

if (_level0.tops_contain.box.hitTest(_root._xmouse, _root._ymouse, false)) {

var distance = _root._xmouse - xcenter;
_x -= ( distance*speed );


if (this._x >= lowX) {
	this._x = lowX;} 
else if (this._x<=highX) {
	this._x = highX;}

}
}
//**************************************************

[/AS]