Error 1009 and I don't know what to do exactly, plz help me

Question

hi
I wish that you could help me
I am a beginner in actionscript 3.0, and I have a main swf file, with a menu and several buttons, when I click on each button, a new swf should be loaded, and the menu is resized and goes to the top left of the page, and if I click on the menu, it should come back..
the problem is that when I click on the first button, everything works well, but when I click on another button, I get this error:
TypeError: Error #1009: Il est impossible d'accéder à la propriété ou à la méthode d'une référence d'objet nul.
    at s_fla::MainTimeline/s_fla::__setProp___id0__Scene1_texte_2()
    at s_fla::MainTimeline/s_fla::frame2()
I understood that the problem is due to the file which is displayed before it has been loaded.
I also found that I have to use the function Event.ADDED_TO_STAGE, but I don't know where to put it??
could you help me please?
here is my code:
function size(e:MouseEvent):void{
    menu_mc.gotoAndPlay(2);
    menu_mc.buttonMode = true;
    menui_mc.addEventListener(MouseEvent.CLICK, showmenu);
    menu_mc.button01_btn.removeEventListener(MouseEvent.CLICK, size);
    menu_mc.button02_btn.removeEventListener(MouseEvent.CLICK, size);
   menu_mc.button03_btn.removeEventListener(MouseEvent.CLICK, size);
addChild (cliploader);
function size(e:MouseEvent):void{
    menu_anatomie_mc.gotoAndPlay(13);
    menu_mc.removeEventListener(MouseEvent.CLICK, showmenu);
    menu_mc.button01_btn.addEventListener(MouseEvent.CLICK, size);
    menu_mc.button02_btn.addEventListener(MouseEvent.CLICK, size);
    menu_mc.button03_btn.addEventListener(MouseEvent.CLICK, size);
    removeChild (cliploader);
menu_mc.button01_btn.addEventListener(MouseEvent.CLICK, loadpage);
menu_mc.button02_btn.addEventListener(MouseEvent.CLICK, loadpage);
menu_mc.button03_btn.addEventListener(MouseEvent.CLICK, loadpage);
menu_mc.button01_btn.page = "file01.swf";
menu_mc.button02_btn.page = "file02.swf";
menu_mc.button03_btn.page = "file03.swf";
function loadpage(e:MouseEvent):void{
    cliploader.myldr.source = e.currentTarget.page;
please tell me what to do exactly
P.S: cliploader is a UI loader which is present on the scene
in my swf files, I have flvplayback which loads a flv files, and I think this is the source of the problem, because I have tried the same thing with a simple swf file which maybe loads quickly, and I didn't get this error
thank you in advance

Answer 1

thanks
I think that the error is in the file that I want to load, in this file I have a flvplayback that I named myplayer, which is in the third frame, and because the video doesn't stop even if I move to another frame, I had to add this code in the third frame
next_btn.visible = true;
prev_btn.visible = true;
myplayer.addEventListener(Event.REMOVED_FROM_STAGE, stopPlay);
function stopPlay(e:Event)
myplayer.stop();
myplayer.stop(); this is line 7 on frame 3
when I publish this file, it works
but when I try to play it from the menu in the main swf file I get the error, how can I fix it please?
can I make this manually, or I'll have the same problem?
as I said, I tried to load different swf files from the main menu and I didn't have this problem (because there were no video players), so I think the problem is caused by the video player?
thank you