title: As3 flash error "Cannot access a property or method of a null object reference"
body: <p>im trying to do a couple of basic games on flash that consist in random numbers but im receiving this error every time i run my scene:</p>
  
  <pre><code>TypeError: Error #1009: Cannot access a property or method of a null object reference.
  at capacitacion_fla::MainTimeline/frame1()
  TypeError: Error #1009: Cannot access a property or method of a null object reference.
  at capacitacion_fla::MainTimeline/frame1()
  at flash.display::MovieClip/gotoAndStop()
  at capacitacion_fla::MainTimeline/fl_ClickToGoToAndStopAtFrame()
  </code></pre>
  
  <p>I am learning flash and as3 and i will appreciate if someone could help me to know whats going on, i also leave you my as3 code that is all placed on frame 1:</p>
  
  <pre><code>stop();
  import com.greensock.*;
  import com.greensock.easing.*;
  import flash.events.MouseEvent;
  import flash.display.MovieClip;
  
  var blitMask1:BlitMask = new   BlitMask(strip1,strip1.x,strip1.y,strip1.width,207,true,true,0xffffff,true);
  var blitMask2:BlitMask = new BlitMask(strip2,strip2.x,strip2.y,strip2.width,207,true,true,0xffffff,true);
  // ------- botones ----------
  
  numerico_btn.addEventListener(MouseEvent.CLICK, fl_ClickToGoToAndStopAtFrame);
  
  function fl_ClickToGoToAndStopAtFrame(event:MouseEvent):void
  {
  gotoAndStop(1);
  }
  
  preguntas_btn.addEventListener(MouseEvent.CLICK, fl_ClickToGoToAndStopAtFrame_2);
  
  function fl_ClickToGoToAndStopAtFrame_2(event:MouseEvent):void
  {
  gotoAndStop(2);
  }
  
  imagenes_btn.addEventListener(MouseEvent.CLICK, fl_ClickToGoToAndStopAtFrame_3);
  
  function fl_ClickToGoToAndStopAtFrame_3(event:MouseEvent):void
  {
  gotoAndStop(3);
  }
  
  
  
  //------- Fin de los botones ----------
  
  //------------ Escena 1 ----------------------------------------------------
  spin_btn.addEventListener(MouseEvent.CLICK, spin);
  
  function spin(event:MouseEvent):void {
  
  var i:int = 1;
  while (i &lt;= 2) {
      var newNumber:Number = (randomNumber(0, 19) * 207) + 4968;
  
      TweenMax.to(this["strip" +i], 2 + (i*.5), {y:strip1.y + newNumber});
      i++;    
  }
  }
  
  function randomNumber(min:Number, max:Number):Number {
  //good
  return Math.floor(Math.random() * (1 + max - min) + min);
  }
  // ----------- fin escena 1 ----------
  
  // ----------- Principio escena 2 -------------------
  
  var blitMask3:BlitMask = new BlitMask( strip1q, strip1q.x, strip1q.y, 392 , strip1q.height, true, true, 0xffff00, true);
  
  
  preguntas_btn.addEventListener(MouseEvent.CLICK, rodarPreguntas);
  
  function rodarPreguntas(event:MouseEvent):void {
  
      preguntas_btn.visible = false;
  
      var newNumber1:Number = (randomNumber1(0, 50)*392) + 21168 ;
      //tween to the relative value of newNumber
      TweenMax.to(strip1q, 4, {x:String(-newNumber1), onComplete:showBtn});       
  }
  
  function showBtn(){
  preguntas_btn.visible = true;
  }
  
  function randomNumber1(min:Number, max:Number):Number {
  //good
  return Math.floor(Math.random() * (1 + max - min) + min);
  }
  
  // ------- Fin escena 2 --------
  </code></pre>
  
  <p>I hope someone can help me figuring this out!</p>