Problem Loading a SWF

Question

I want to load a SWF form another SWF and a have one error:
TypeError: Error #1009: Cannot access a property or method of
a null object reference.
at MoverBall$iinit()
Any help?
here is the actionscript code:
package {
import flash.display.*;
import flash.events.*;
import flash.events.KeyboardEvent;
import flash.ui.Keyboard;
import flash.geom.Point;
public class MoverBall extends MovieClip{
private var gameSprite:Sprite;
private var ball:Ball2;
private var xpos:Number = 0;
private var ypos:Number = 0;
private var zpos:Number = 0;
private var vx:Number = 0;
private var vy:Number = 0;
private var vz:Number = 0;
private var friction:Number = .95;
private var fl:Number = 250;
private var vpX:Number = stage.stageWidth / 2;
private var vpY:Number = stage.stageHeight / 2;
public function MoverBall(){
// INICIALIZAR SPRITE
gameSprite = new Sprite();
ball = new Ball2();
stage.addChild(gameSprite);
gameSprite.addChild(ball);
addEventListener(Event.ENTER_FRAME, onEnterFrame);
stage.addEventListener(KeyboardEvent.KEY_DOWN, onKeyDown);
function onEnterFrame(event:Event):void{
xpos += vx;
ypos += vy;
zpos += vz;
vx *= friction;
vy *= friction;
vz *= friction;
if(zpos > -fl){
var scale:Number = fl / (fl + zpos);
ball.scaleX = ball.scaleY = scale;
ball.x = vpX + xpos * scale;
ball.y = vpY + ypos * scale;
ball.setCentro(new Point(ball.x+10, ball.y+10));
ball.visible = true;
else{
ball.visible = false;
function onKeyDown(event:KeyboardEvent):void{
switch(event.keyCode){
case Keyboard.UP :
vy -= 1;
break;
case Keyboard.DOWN :
vy += 1;
break;
case Keyboard.LEFT :
vx -= 1;
break;
case Keyboard.RIGHT :
vx += 1;
break;
case Keyboard.SHIFT :
vz += 1;
break;
case Keyboard.CONTROL :
vz -= 1;
break;
default :
break;
function getBall(){
return ball;
And the code in my FLA is:
// Request the content
var url:URLRequest = new URLRequest("Ball2.swf");
// Create a loader object
var loader:Loader = new Loader();
// Load the content
loader.load(url);
// Add loader into the Display List
addChild(loader);

Answer 1

here is the code of Ball2
package {
import flash.display.Sprite;
import flash.geom.Point;
import flash.display.*;
public class Ball2 extends MovieClip{
private var centro:Point;
private var aux:int;
public function Ball2(){
graphics.beginFill(0xff0000);
graphics.drawCircle(0,0,10);
graphics.endFill();
this.x=100;
this.y=100;
centro = new Point(this.x+10, this.y+10);
aux=1234;
public function getCentro(){
return centro;
public function getVar():int{
return aux;
public function setCentro(c:Point){
centro=c;
}