Error #1009: Cannot access a property or method of a null object reference

1

I can’t solve this, i need help.

I am trying to load another b.swf into this a.swf
if i try to load a swf without class it works fine.
a.swf have no class, but b.swf have.
I encounter this error.

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at MyGame()

What is the solution?
a.fla


stop();

function startLoad()
{
var imageRequest:URLRequest = new URLRequest("b.swf");
var imageLoader:Loader = new Loader();
imageLoader.load(imageRequest);
addChild(imageLoader);
}

function onCompleteHandler(loadEvent:Event)
{
        addChild(loadEvent.currentTarget.content);
}
function onProgressHandler(mProgress:ProgressEvent)
{
var percent:Number = mProgress.bytesLoaded/mProgress.bytesTotal;
trace(percent);
}
startLoad();

Mygame.as


package {
	import flash.display.MovieClip
	import flash.display.Sprite
	import flash.display.Bitmap
	import flash.display.BitmapData
	import flash.display.Graphics
	import flash.events.Event
	import flash.events.MouseEvent
	import flash.utils.ByteArray
	import flash.utils.setInterval
	import flash.utils.setTimeout
	import flash.geom.Point
	import flash.text.TextField
	import flash.display.BlendMode
	import flash.display.StageScaleMode
	import flash.display.StageAlign
	import flash.text.TextFormat
	
	import playerio.*
	import sample.ui.Prompt
	import sample.ui.Chat
	import sample.ui.Lobby
	
	public class MyGame extends MovieClip{
		private var connection:Connection
		private var lobby:Lobby
		private var questions:Array=new Array();
		private var answers:Array=new Array();

		[Embed(source="c.xml", mimeType="application/octet-stream")]
		private static const MyData:Class;
		
		function MyGame(){
			stop();
			
			
			PlayerIO.connect(
				stage,								//Referance to stage
				"quiz-sfhwfbj70ectvbcjazv2tw",	//Game id (Get your own at playerio.com)
				"public",							//Connection id, default is public
				"name",						//Username
				"",									//User auth. Can be left blank if authentication is disabled on connection
				handleConnect,						//Function executed on successful connect
				handleError							//Function executed if we recive an error
			);   
			stage.scaleMode = StageScaleMode.NO_SCALE
			stage.align = StageAlign.BOTTOM
		}
		
		private function handleConnect(client:Client):void{
			trace("Sucessfully connected to player.io");
			
			//Set developmentsever (Comment out to connect to your server online)
			client.multiplayer.developmentServer = "localhost:8184";
			
			//Create pr join the room test
			client.multiplayer.createJoinRoom(
				"",							//Room id. If set to null a random roomid is used
				"bounce",							//The game type started on the server
				false,								//Should the room be visible in the lobby?
				{},									//Room data. This data is returned to lobby list. Variabels can be modifed on the server
				{},
				handleJoin,							//Function executed on successful joining of the room
				handleError							//Function executed if we got a join error
			);
			//Create lobby
			lobby = new Lobby(client, "mygame", handleJoin, handleError)

			//Show lobby (parsing true hides the cancel button)
			lobby.show(true);
		}
		
		
		private function handleJoin(connection:Connection):void{
			trace("Sucessfully connected to the multiplayer server");
						
			var byteArray:ByteArray = new MyData() as ByteArray;
			var xml:XML = new XML(byteArray.readUTFBytes(byteArray.length));
			var loop = 5;
			
			for (var i=0;i<loop;i++)
			{
				questions*=xml.ques*.q1;
				//questions*=loop;
				answers*=[xml.ques*.op1,xml.ques*.op2,xml.ques*.op3];
				//answers*=loop;
			}
			gotoAndStop(2);
			stop();

			/*
			trace(questions[1]);
			trace(answers[1]);
			trace(answers[1][0]);
			trace(answers[1][1]);
			trace(answers[1][2]);
			*/
						//Add chat to game
			var chat:Chat = new Chat(stage, connection);
			
			//Add listener for messages of the type "hello"
			connection.addMessageHandler("hello", function(m:Message){
				trace("Recived a message with the type hello from the server");			 
			})
			
			//Add message listener for users joining the room
			connection.addMessageHandler("UserJoined", function(m:Message, userid:uint){
				trace("Player with the userid", userid, "just joined the room");
			})
			
			//Add message listener for users leaving the room
			connection.addMessageHandler("UserLeft", function(m:Message, userid:uint){
				trace("Player with the userid", userid, "just left the room");
			})
			
			//Listen to all messages using a private function
			connection.addMessageHandler("*", handleMessages)
			
		}
		
		private function handleMessages(m:Message){
			trace("Recived the message", m)
		}
		
		private function handleDisconnect():void{
			trace("Disconnected from server")
		}
		
		private function handleError(error:PlayerIOError):void{
			trace("got",error)
			gotoAndStop(4);

		}
	}	
}