Loaded swf with button , not communicating to main timeline

Question

my main stage/timeline has a UILoader "UILoaderOne" and
another one "UIloaderTwo".
i have some buttons on the main stage which pull up some
images into the UILoaderOne.
these work fine and look like this.
//BEGIN BUTTONCODE\\
//button to load image into loader "loaderOne" x01_btn and
x01_ldr, thumb image is "x01.jpg and main image is p01.jpg\\
//crop thumb image to size 50px tall by whatever wide and
resize loaderButton if needed, main image will resize
proportionatly\\
x01_btn.addEventListener(MouseEvent.CLICK, onClick);
function onClick(event:MouseEvent):void
//import fl.containers.UILoader;
import fl.controls.Label;
import fl.controls.ProgressBar;
var url:String = "assets/01.jpg";
//var myUILoader:UILoader //= new UILoader();
myUILoader.unload();
myUILoader.autoLoad = false;
myUILoader.source = url;
//myUILoader.move(10, 10);
myUILoader.scaleContent = true;
myUILoader.load();
var myProgressBar:ProgressBar = new ProgressBar();
myProgressBar.source = myUILoader;
myProgressBar.setSize(100, 10);
myProgressBar.move(myUILoader.x+340, myUILoader.y+250)
myProgressBar.addEventListener(ProgressEvent.PROGRESS,
progressHandler);
myProgressBar.addEventListener(Event.COMPLETE,
completeHandler);
addChild(myProgressBar)
var myLabel:Label = new Label();
myLabel.text = ". . . . . X . . . . . ";
myLabel.autoSize = TextFieldAutoSize.LEFT;
myLabel.move(myProgressBar.x, myProgressBar.y +
myProgressBar.height);
addChild(myLabel);
function progressHandler(event:ProgressEvent):void {
//trace("progress:", event.bytesLoaded, event.bytesTotal,
int(event.currentTarget.percentComplete) + "%");
//myLabel.text = event.bytesLoaded + " of " +
event.bytesTotal + " bytes loaded.";
myLabel.text = ("progress:", event.bytesLoaded,
event.bytesTotal, int(event.currentTarget.percentComplete) + "%")
//myLabel.text =
Math.round((event.bytesLoaded/event.bytesTotal)*100) +"%";
function completeHandler(event:Event):void {
trace("complete:");
myProgressBar.removeEventListener(ProgressEvent.PROGRESS,
progressHandler);
myProgressBar.removeEventListener(Event.COMPLETE,
completeHandler);
removeChild(myProgressBar);
removeChild(myLabel);
//addChild(myUILoader);
//trace("typeMe");
//end BUTTONCODE\\
//end BUTTONCODE\\
the second Loader "UILoaderTwo" auto loads another swf file
with the INTENT to load from buttons, images into the ULLoader
"UILoaderOne" which is on the main timeline.
this part is failing
the error i get in Output window is
TypeError: Error #1009: Cannot access a property or method of
a null object reference.
at sOne_fla::MainTimeline/onClickz()
the swf that loads is sOne.swf
and it has code of this
z01_btn.addEventListener(MouseEvent.CLICK, onClickz);
function onClickz(event:MouseEvent):void
import fl.containers.UILoader;
import fl.controls.Label;
import fl.controls.ProgressBar;
var url:String = "assets/xx.jpg";
var myUILoader:UILoader //= new UILoader();
myUILoader.unload();
myUILoader.autoLoad = false;
myUILoader.source = url;
//myUILoader.move(10, 10);
myUILoader.scaleContent = true;
myUILoader.load();
var myProgressBar:ProgressBar = new ProgressBar();
myProgressBar.source = myUILoader;
myProgressBar.setSize(100, 10);
myProgressBar.move(myUILoader.x+340, myUILoader.y+250)
myProgressBar.addEventListener(ProgressEvent.PROGRESS,
progressHandler);
myProgressBar.addEventListener(Event.COMPLETE,
completeHandler);
addChild(myProgressBar)
var myLabel:Label = new Label();
myLabel.text = ". . . . . X . . . . . ";
myLabel.autoSize = TextFieldAutoSize.LEFT;
myLabel.move(myProgressBar.x, myProgressBar.y +
myProgressBar.height);
addChild(myLabel);
function progressHandler(event:ProgressEvent):void {
//trace("progress:", event.bytesLoaded, event.bytesTotal,
int(event.currentTarget.percentComplete) + "%");
//myLabel.text = event.bytesLoaded + " of " +
event.bytesTotal + " bytes loaded.";
myLabel.text = ("progress:", event.bytesLoaded,
event.bytesTotal, int(event.currentTarget.percentComplete) + "%")
//myLabel.text =
Math.round((event.bytesLoaded/event.bytesTotal)*100) +"%";
function completeHandler(event:Event):void {
trace("complete:");
myProgressBar.removeEventListener(ProgressEvent.PROGRESS,
progressHandler);
myProgressBar.removeEventListener(Event.COMPLETE,
completeHandler);
removeChild(myProgressBar);
removeChild(myLabel);
//addChild(myUILoader);
//trace("typeMe");
//end BUTTONCODE\\
//end BUTTONCODE\\

Answer 1

well, I'm such a novice to begin with.
the loader is actually placed on stage manually, and instance
named manually so a lot of that code is may not be needed,
i do a lot of trial and error technique
it is all personal stuff
one guess i have is to set up a listner as to when the sOne
is loaded, and then get a way to communicate to each other?
how?