Timeline animation, TypeError: Error #1009

programming flash
1

I am doing a simple timeline set here, each frame has a movieclip and inside the movieclip is a button called next_btn, which will take it to the next frame.

Each frame is labelled.


stop();

/* ------------------ Section A ------------------------------- */

start_btn.addEventListener(MouseEvent.CLICK, goT1);

function goT1(event:MouseEvent){
	gotoAndStop("t1");	
}

t1_mc.next_btn.addEventListener(MouseEvent.CLICK, goT2);

function goT2(event:MouseEvent){
	gotoAndStop("t2");	
}

t2_mc.next_btn.addEventListener(MouseEvent.CLICK, goT3);

function goT3(event:MouseEvent){
	gotoAndStop("t3");	
}

t3_mc.next_btn.addEventListener(MouseEvent.CLICK, goT4);

function goT4(event:MouseEvent){
	gotoAndStop("t4");	
}

t4_mc.next_btn.addEventListener(MouseEvent.CLICK, goT5);

function goT5(event:MouseEvent){
	gotoAndStop("t5");	
}

This code is in the main timeline on the first frame.

Why do I still get this OUTPUT error?

TypeError: Error #1009: Cannot access a property or method of a null object reference. at beginner_fla::MainTimeline/frame1()

Thank you