Skip to next frame from a checkbox that is located in a scrollpane .

Can you help me i have this code like this

import flash.events.MouseEvent;

import flash.display.MovieClip;

public class testNN extends MovieClip{

MovieClip (SP.content).btn.addEventListener(MouseEvent.CLICK, goForward);

function goForward(event:MouseEvent):void {

    MovieClip (CheckBox.content).nextFrame();

}

}

;

i have this errors :

Scene 1, Layer 'Layer 1', Frame 1, Line 7 1114: The public attribute can only be used inside a package.

Thanks