title: Flash Error #1009 for a Button
body: <p>I'm new to AS3, and I keep getting Error #1009 when I try to add a button. From some reading I did I gather it is when I reference something I think exists but that really doesn't, except I have added a correct instance_name, and this did not happen for any of my other buttons.</p>
  
  <p>Below is my code:</p>
  
  <pre><code>stop();
  
  //buttons
  Erhu_btn.addEventListener(MouseEvent.MOUSE_DOWN, Erhu_func);
  Flute_btn.addEventListener(MouseEvent.MOUSE_DOWN, Flute_func);
  Guzheng_btn.addEventListener(MouseEvent.MOUSE_DOWN, Guzheng_func);
  Ruan_btn.addEventListener(MouseEvent.MOUSE_DOWN, Ruan_func);
  Yangqin_btn.addEventListener(MouseEvent.MOUSE_DOWN, Yangqin_func);
  Compose_btn.addEventListener(MouseEvent.MOUSE_DOWN, Compose_func);
  Intro_btn.addEventListener(MouseEvent.MOUSE_DOWN, Intro_func);
  
  //function definitions
  function Erhu_func(event:MouseEvent):void {
      gotoAndStop("Erhu"); 
  }
  function Flute_func(event:MouseEvent):void {
      gotoAndStop("Flute"); 
  }
  function Guzheng_func(event:MouseEvent):void {
      gotoAndStop("Guzheng"); 
  }
  function Ruan_func(event:MouseEvent):void {
      gotoAndStop("Ruan"); 
  }
  function Yangqin_func(event:MouseEvent):void {
      gotoAndStop("Yangqin"); 
  }
  function Compose_func(event:MouseEvent):void {
      gotoAndStop("Compose");
  }
  function Intro_func(event:MouseEvent):void {
      gotoAndStop("Intro"); 
  }
  </code></pre>
  
  <p>All the buttons work except for the Intro_btn. I know it's probably a really simple mistake, but I can't figure it out, and I would really appreciate any light you could shed on my problem!</p>