I am sorry for my a little mistake.

please find the fellowing code in ActionScript frame.and Change it.

It s on 64 line,change this: 
var percent_scrolled = (dragger._y -btnup._height)/(scrollHeight-dragger._height); 

as:

var percent_scrolled = (dragger._y -btnup._y -btnup._height)/(scrollHeight-dragger._height);

Thanks.