New to action script and getting: TypeError: Error #1009: Cannot access a property or method of a nu

Question

I am getting this message in the output tab for buttons that I am trying to create.  Here's the code:
import flash.events.MouseEvent;
stop();
function goHome(myEvent:MouseEvent):void {
gotoAndStop("home");
SoundMixer.stopAll();
function goAbout(myEvent:MouseEvent):void {
gotoAndStop("about");
SoundMixer.stopAll();
function goBusiness(myEvent:MouseEvent):void {
gotoAndStop("business");
SoundMixer.stopAll();
function goContact(myEvent:MouseEvent):void {
gotoAndStop("contact");
SoundMixer.stopAll();
function goArchives(myEvent:MouseEvent):void {
gotoAndStop("archives");
SoundMixer.stopAll();
function goBioTech(myEvent:MouseEvent):void {
gotoAndStop("bioTech");
SoundMixer.stopAll();
function goRealEstate(myEvent:MouseEvent):void {
gotoAndStop("realEstate");
SoundMixer.stopAll();
function goTechnology(myEvent:MouseEvent):void {
gotoAndStop("technology");
SoundMixer.stopAll();
function goEnergy(myEvent:MouseEvent):void {
gotoAndStop("energy");
SoundMixer.stopAll();
home_btn.addEventListener(MouseEvent.CLICK, goHome);
about_btn.addEventListener(MouseEvent.CLICK, goAbout);
business_btn.addEventListener(MouseEvent.CLICK, goBusiness);
contact_btn.addEventListener(MouseEvent.CLICK, goContact);
archives_btn.addEventListener(MouseEvent.CLICK, goArchives);
bioTech_btn.addEventListener(MouseEvent.CLICK, goBioTech);
realEstate_btn.addEventListener(MouseEvent.CLICK, goRealEstate);
technology_btn.addEventListener(MouseEvent.CLICK, goTechnology);
energy_btn.addEventListener(MouseEvent.CLICK, goEnergy);
I ran the debugger and got this:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at peakInsights_fla::MainTimeline/frame1()[peakInsights_fla.MainTimeline::frame1:48]
I guess it's telling me there's a problem with line 48 but what?
The home, about, business, contact, and archives button works. On the business page there are the remaining buttons biotech, technology, real estate, and energy. when i test it; i get the finger but the buttons don't work. this is my first flash site so I'am new, new.

Answer 1

I followed the steps and read some of your comments on the same top topic in another thread. When I put it on the first frame it was okay but the next button on that page had the same problem.  So what I am guessing is that I have to either create a document class or put the actions where the buttons are.  Am I understanding that correctly?  In the other thread in which you helped someone else; there was so comments about document class.  I found a tutorial on it and the way I understand it is that it you can put you actions in an external document.  But you have to include in the event listener the frame in which you want that action to happen.
Thaks for your help.  And patience.