Attempt to move main timeline from inside a movie clip breaks menu buttons.

Question

I am attempting to have the main timeline move from a stopped position over a movie clip to frame 1, where my start menu is.
The code I'm using does move the timeline but in doing so it somehow breaks the 4 buttons I have in frame 1.
My code in the movie clip:
stop()
function replayMovie(event:MouseEvent):void
MovieClip(parent).gotoAndStop(1);
Menu.addEventListener(MouseEvent.CLICK, replayMovie);
My code in frame 1 of the main timeline:
stop();
function bo(event:MouseEvent):void
gotoAndPlay(21)
SoundMixer.stopAll()
espesp.addEventListener(MouseEvent.CLICK, bo);
function ho(event:MouseEvent):void
gotoAndPlay(31)
SoundMixer.stopAll()
espeng.addEventListener(MouseEvent.CLICK, ho);
function yo(event:MouseEvent):void
gotoAndPlay(41)
SoundMixer.stopAll()
engesp.addEventListener(MouseEvent.CLICK, yo);
function go(event:MouseEvent):void
gotoAndPlay(51)
SoundMixer.stopAll()
engeng.addEventListener(MouseEvent.CLICK, go);
The error output when I use my Menu button at the end of the movie clip.
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at SSubjunctiveProjNewgrounds_fla::MainTimeline/frame1()
at flash.display::MovieClip/gotoAndStop()
at SSubjunctiveProjNewgrounds_fla::Esp_5/replayMovie()
Any help would be greatly appreciated.

Answer 1

For the sake of space, I'll leave out all the package declarations and class declarations and just talk about the functions.
First, the Game class, it has two functions.  The first one is the constructor function and it launches at the beginning of the game:  First the Game function:
public function Game():void
//Game code goes here
}//Game
We want to listen for someone to click the mouse on the MenuPage, so lets create a new MenuPage and add a listener to the button contiained within it.
public function Game():void
menuPage = new MenuPage;
menuPage.startButton.addEventListener(MouseEvent.CLICK, startGame);
addChild(menuPage);
}//Game
You will notice that before I declared a variable var menuPage:MenuPage, but that's all I did was declare it.  I didn't really make a new instance of it, I just set aside space for it.  In the first line within the Game function, I'm actually turning that variable into a new instance of a MenuPage.
We don't have a picture of this imaginary menuPage instance, but lets' assume that in our MenuPage MovieClip in the library, we created a SimpleButton called startButton.  Here, I'm adding an EventListener that patiently waits for someone to click that button.  Once we receive that event, Flash is told to call the startGame function.
As you get better at this, you'll get into custom events, and the eventListener for the button will exist in the MenuPage class file, or even in another class file that you create just for the button.  Something like StartButton.as  But for now, we can do it as above.
Now the startGame function:
          public function startGame(evt:MouseEvent):void
//Remove the start Page
//Add the zombie
//Add the gun
}//startGame
And we'll replace those comments with real code.  It follows along with what we just did above.
public function startGame(evt:MouseEvent):void
zombie = new Zombie;
addChild(zombie);
gun = new Gun;
addChild(gun);
And we also want to clean up some by removing the menuPage, and throwing out the eventListener.
public function startGame(evt:MouseEvent):void
zombie = new Zombie;
addChild(zombie);
gun = new Gun;
addChild(gun);
menuPage.startButton.removeEventListener(MouseEvent.Click,startGame);
removeChild(menuPage);
}//startGame
Now our Game class is complete.
The Zombie Class
public function zombieWalk(evt:Event):void
this.addEventListener(Event.ENTER_FRAME,zombieWalk);
this.x = this.x + 10;
}//zombieWalk
Notice we've added a function to the Zombie Class.
The first function adds an EventListener to the zombie.  We can use the word this and actionScript knows we're talking about the zombie that the class is written for.  This listener fires off every frame.  If our FLA file is set to 12fps, then 12 times every second it will call on the zombieWalk function.
The zombie walk function moves the zombie 10 pixels to the right every time the function is called.
On a more advanced level, you'll want to add animation in the MovieClip to move the zombie legs.  You'll also want to use Timer events to space out how often the funtion fires and not ENTER_FRAME events.  And you'll want to use a static constant to establish how far the zombie moves.  We have it now set to 10 pixels, but that can get irritating if we want to change that value later.  But again, baby steps.
And finally, the Gun class
public function Gun():void
this.addEventListener(MouseEvent.CLICK, fireGun);
}//function
public function fireGun(evt:MouseEvent):void
this.gotoAndPlay(2);
}//fireGun
First we add an EventListener for when someone clicks on the gun.  Once this happens, the listener calls on the fireGun function.
The fireGun function takes advantage of the frames within the Gun MovieClip.  Say we have three frames in the Gun MovieClip.  The first is just a picture of the gun.  The second is the gun with a flash coming out of the nozzle.  And the third is the gun at rest again.  The line this.gotoAndPlay(2) sends the gun to the second frame with the flash graphic.
For this to work, each frame in the Gun MovieClip has to have some stop and play commands.
But.. you said no code on our timeline!! Liar!
I know.  This is the exception.  You will need basic stop() commands and gotoAndPlay commands to loop animations.  Any MovieClip that has more than one frame will need something to control it.
So our Gun MovieCLip has the following:
Frame 1: stop();
Frame 2: no actionScript... and I mean nothing, not even the words, "no actionScript"
Frame 3: gotoAndStop(1);
This will loop the gun to the beginning and wait for the next time the user clicks the gun.
Advanced features of the Gun class might include a Bullet.as sub-class that creates a bullet MovieClip to fly across the screen.  Sound to play when the shooting takes place.  Object collision detection to see if the bullet hits the target.  And a means by which a custom event will tell the Game.as class that a zombie has been hit and it should be removed from the stage.
As you go down the rabbit hole of ActionScript 3, you will find yourself at a point where it's just a matter of getting the syntax right for all the built in functions and classes.  Arrays, Loaders, casting variable types.. all that stuff will come.
I hope this has been helfpul.  It's been on my to-do list for a long time.  When I first started out, no one could provide me with basic answers for how all these classes and whatnot worked.  After teaching myself AS3 for 2 years and reading a gabillion books, I think I've gotten to a point where I'm pretty comfortable with it all.