hello as2 image scroll buttons. I can't get the scroll to work

Thank you in advance for your help. I am building an vertical image scroll buttons in AS2. but I cant get the scroll to work. Can you please look at my script and see if I am missing something. Thank you again.

topEdge=mask_mc._y;

maskHeight=mask_mc._height;

sliderHeight=slider_mc._height;

ratio=maskHeight/(sliderHeight-maskHeight)

//trace(ratio)

targY=slider_mc._y;

slider_mc.onEnterFrame=function(){

  this._y+=(targY-this._y)/5;

}

slider_mc.onMouseMove=function(){

  if(mask_mc.hitTest(_ymouse,_xmouse,false)){

    targY=topEdge-(mask_mc._ymouse/ratio)

    updateAfterEvent();

  }

}