Xml gallery

Question

I have a gallery that malfunctions some of the time when you try to explore my website. it is some what complicated to explain so I will describe my set up with the assistance of my code.
SWF file contains this code on the hompage frame:
////BUTTONS//////
stop();
//-----Navigation Buttons ------------//
home_btn.addEventListener(MouseEvent.CLICK, homeclick);
function homeclick(event:MouseEvent):void
gotoAndStop(2);
if(img_holder.stage)
removeChild(img_holder);
port_btn.addEventListener(MouseEvent.CLICK, portclick);
function portclick(event:MouseEvent):void
gotoAndStop(3);
abou_btn.addEventListener(MouseEvent.CLICK, abouclick);
function abouclick(event:MouseEvent):void
gotoAndStop(8);
if(img_holder.stage)
removeChild(img_holder);
blog_btn.addEventListener(MouseEvent.CLICK, blogclick);
function blogclick(event:MouseEvent):void
gotoAndStop(9);
if(img_holder.stage)
removeChild(img_holder);
cont_btn.addEventListener(MouseEvent.CLICK, contclick);
function contclick(event:MouseEvent):void
gotoAndStop(10);
if(img_holder.stage)
removeChild(img_holder);
On my gallery/home page the code looks like:
/////gallery buttons/////////
gal1_btn.addEventListener(MouseEvent.CLICK, gal1click);
function gal1click(event:MouseEvent):void
gotoAndStop(4);
gal2_btn.addEventListener(MouseEvent.CLICK, gal2click);
function gal2click(event:MouseEvent):void
gotoAndStop(5);
gal3_btn.addEventListener(MouseEvent.CLICK, gal3click);
function gal3click(event:MouseEvent):void
gotoAndStop(6);
gal4_btn.addEventListener(MouseEvent.CLICK, gal4click);
function gal4click(event:MouseEvent):void
gotoAndStop(7);
once you've selected a gallery it takes you to that specific gallery.. i have four of them, but gal1 is the only one with as3 because i wanted to get the bugs sorted out before continuing with the other three. The as3 code lookes like this in gallery1:
var xml:XML = new XML();
var img_count:uint;
var loader:URLLoader = new URLLoader();
var img_holder:Sprite=new Sprite();
var sw:Number=stage.stageWidth;
addChild(img_holder);
function xmlloaded(e:Event):void
xml=XML(e.target.data);
img_count = xml.img.length()-1;
for (var i:uint = 0; i<img_count; i++)
  var thumb:Sprite=new createThumb(img_holder,String(xml.img[i].@thumburl),String(xml.img[i].@mainurl));
  thumb.x=130*i;
  img_holder.addChild(thumb);
stage.addEventListener(Event.ENTER_FRAME,mousescroll);
function mousescroll(e:Event):void
var ihw:Number = (img_holder.width-sw+350)*-1;
var percent:Number = 175+(mouseX/sw)*(ihw);
img_holder.x=percent;
loader.load(new URLRequest('photogallery.xml'));
loader.addEventListener(Event.COMPLETE,xmlloaded);
this code calls to an outside xml file, which looks like this:
var img_holder:Sprite=new Sprite();
var thumb:Sprite=new createThumb(img_holder,'smallimage/file.png','largeimage/file.png');
thumb.x=205*i;
img_holder.addChild(thumb);
addChild(img_holder);
package {
import flash.display.Loader;
import flash.display.Sprite;
import flash.display.Bitmap;
import fl.transitions.Tween;
import fl.transitions.TweenEvent;
import fl.transitions.easing.*;
import flash.events.MouseEvent;
import flash.events.Event;
import flash.net.URLRequest;
public class createThumb extends Sprite {
private var arraytween:Array = new Array();
private var thumb_loader:Loader;
private var photo_loader:Loader;
private var thumb_url:String;
private var photo_url:String;
private var thumb_bit:Bitmap;
private var photo_bit:Bitmap;
private var mother:Sprite;
private var thumb_btn:Sprite;
public function createThumb(childof:Sprite,thumburl:String,photourl:String) {
mother=childof;
thumb_url=thumburl;
photo_url=photourl;
loadthumb();
private function loadthumb():void {
thumb_loader = new Loader();
thumb_loader.load(new URLRequest(thumb_url));
thumb_loader.contentLoaderInfo.addEventListener(Event.COMPLETE,displaythumb);
private function displaythumb(e:Event):void {
thumb_btn = new Sprite();
thumb_bit= new Bitmap();
thumb_btn.y=(stage.stageHeight-thumb_btn.height)/1.25;
thumb_btn.graphics.beginFill(0x000000,0);
thumb_btn.graphics.drawRect(0,0,125,125);
thumb_btn.graphics.endFill();
thumb_bit=e.target.content as Bitmap;
thumb_bit.y=(stage.stageHeight-thumb_bit.height)/1.045;
thumb_btn.width=thumb_btn.height=thumb_bit.width=thumb_bit.height=125;
thumb_bit.smoothing=true;
addChild(thumb_bit);
addChild(thumb_btn);
thumb_btn.addEventListener(MouseEvent.CLICK,loadphoto);
private function loadphoto(e:Event):void {
arraytween.push(new Tween(mother,"y",Regular.easeOut,mother.y,0,.5,true));
photo_loader = new Loader();
photo_loader.load(new URLRequest(photo_url));
photo_loader.contentLoaderInfo.addEventListener(Event.COMPLETE,displayphoto);
private function displayphoto(e:Event):void {
stage.addEventListener(MouseEvent.CLICK,closephoto);
photo_bit= new Bitmap();
photo_bit=e.target.content as Bitmap;
photo_bit.smoothing=true;
photo_bit.x=(192);
photo_bit.y=(110);
stage.addChild(photo_bit);
private function closephoto(e:Event):void
arraytween.push(new Tween(mother,"y",Strong.easeOut,mother.y,0,.5,true));
arraytween[arraytween.length-1].addEventListener(TweenEvent.MOTION_FINISH,cleartween);
photo_loader.unload();
if(photo_bit.stage)
stage.removeChild(photo_bit);
stage.removeEventListener(MouseEvent.CLICK,closephoto);
//if (photo_bit != null)
          // stage.removeChild(photo_bit);
private function cleartween(e:TweenEvent):void
arraytween=[];
thats all of it.. my specific problem can be seen at www.bradleyferguson.com
play around with the 1st gallery which is located under portfolio and is in red.. you'll see what im talking about.

Answer 1

the problem is this line of code ...
if(photo_bit.stage)
stage.removeChild(photo_bit);
it says that it is a null reference when i click on a button, but when i click on the screen it works without error.. it also works when i click on the portfolio button, but like i said when i click on any other button i get an error.