Call function in imported class from main class

1

Hello, its probably been asked (X) times.
However I cannot spot my mistake here.

I’ve read : http://greenethumb.com/article/23/understanding-root-and-the-document-class-in-as3

Which helps me perfectly to call a function from the “imported” class inside the documentclass.

But I can’t seem to manage to trigger a function inside my imported class:
This class is functionality for a button:
aka i want to show some text inside that specific button:

main.as:

public function ldr_onComplete( event:Event ):void
		{
			var variables:URLVariables = new URLVariables(event.target.data);
			ldr.removeEventListener(Event.COMPLETE, ldr_onComplete);
var SAVE:save_button = new save_button();
			SAVE.COMPLETED();
		}

save_button.as

public function COMPLETED():void 
		{
			trace ("save DONE");
			saveBool = true;
			
		}

This traces the following error:


TypeError: Error #1009: Kan geen eigenschap of methode benaderen via een verwijzing naar een object dat null is.
	at classes.buttons::save_button()
	at main2/ldr_onComplete()
	at flash.events::EventDispatcher/dispatchEventFunction()
	at flash.events::EventDispatcher/dispatchEvent()
	at flash.net::URLLoader/onComplete()

So going back to that greenethumb blog post.
I am doing the exact same thing (i think) as he mentioned with:
child.traceRoot(); inside his main class…

any help is more then welcome. it baffles me.
cheers