How do I stop Pan effect?

Basically, I’m having this huge image that moves around depending on where your mouse is. Awesome, however, I wanted to make some clickable areas that would load in movie clips. Problem, the background image still moves around even though you just loaded in a new MC in a new layer.

Here is the code (which I stole from tutorials, sorry to the author, I can’t remember your name, but you rawk!)

function imagePan(target:MovieClip, velocity:Number):Void {
dHori = _root._xmouse / Stage.width, dVert = _root._ymouse / Stage.height;
hPoint = Math.round(-(rHori * dHori)), vPoint = Math.round(-(rVert * dVert));
rHori = target._width - Stage.width, rVert = target._height - Stage.height;
onEnterFrame = function ():Void {
target._x += Math.ceil((hPoint - target._x) * (velocity / 100));
target._y += Math.ceil((vPoint - target._y) * (velocity / 100));
onMouseMove = function ():Void {
imagePan(MY_MC, 5);

**And this is what I put in the button:

**on (release) {
imagePan(this._parent.MY_MC, 0);
}Any help much appreciated, and hopefully I get to keep my job!