Slider problem

Hey everyone,

I’m making a slider which will eventually control the alpha levels of a movieclip of mine but I’m having trouble controlling the parameters in the startDrag() function. Here is the code:
[AS]borderBottom = 0;
borderSide = 0;
sliderMC.onPress = function(){
this.startDrag(true,borderSide,borderMC._height, borderMC._width, borderBottom);
sliderMC.onRelease = function(){
This seems to work ok, however, the problem is encountered when I go to drag the MC…for some unknown reason it ventures off its slider bar and goes to the left. I will attach the .fla and if anyone could help me it would be great!

Thanks A Lot