Help on Timeline / Playhead movement

1

Hi all,

I have 3 movieClips on main timeline named, mat01mc,mat02mc,mat04mc. Also I have 5 buttons to control the play and pause, but I get errors message when click the buttons : TypeError: Error #1009: Cannot access a property or method of a null object reference.
at matrix0904_simplfied_fla::MainTimeline/gItems()

My code is as below :

===========================================

goStart.addEventListener(MouseEvent.CLICK,gStart);

function gStart(e:MouseEvent):void {
gotoAndPlay(“start”)
mat01mc.gotoAndPlay(1);
}

goMile.addEventListener(MouseEvent.CLICK,gMile);

function gMile(e:MouseEvent):void {
gotoAndPlay(“itemL”)
mat02mc.gotoAndPlay(1);
}

goItems.addEventListener(MouseEvent.CLICK,gItems);

function gItems(e:MouseEvent):void {
gotoAndPlay(“items”)
mat04mc.gotoAndPlay(1);
}

stopM.addEventListener(MouseEvent.CLICK,gStop);

function gStop(e:MouseEvent):void {
mat01mc.stop();
mat02mc.stop();
mat04mc.stop();
stop();
}

playM.addEventListener(MouseEvent.CLICK,gPlay);

function gPlay(e:MouseEvent):void {
mat01mc.play();
mat02mc.play();
mat04mc.play();
play();
}

===========================================================

Would you tell me what’s wrong ? all buttons are located at the main timeline.

Thank you in advance.

Florence