What is TypeError: Error #1009: Cannot access a property or method of a null object reference.

it warn me message.

 

typeerror: error #1009: cannot access property or method of null object reference.

@ methodinfo-9()

typeerror: error #1009: cannot access property or method of null object reference.

@ methodinfo-12()

 

mycode here:

 

var count:number = 0;
var objectoriginalx3:number;
var objectoriginaly3:number;

this.stop();

date.buttonmode = true;
date.addeventlistener(mouseevent.mouse_down, pickupobject3);
date.addeventlistener(mouseevent.mouse_up, dropobject3);

authorq3.buttonmode = true;
authorq3.addeventlistener(mouseevent.mouse_down, pickupobject3);
authorq3.addeventlistener(mouseevent.mouse_up, dropobject3);

titleq3.buttonmode = true;
titleq3.addeventlistener(mouseevent.mouse_down, pickupobject3);
titleq3.addeventlistener(mouseevent.mouse_up, dropobject3);

publication.buttonmode = true;
publication.addeventlistener(mouseevent.mouse_down, pickupobject3);
publication.addeventlistener(mouseevent.mouse_up, dropobject3);

function pickupobject3(event:mouseevent):void {
event.target.startdrag(true);
event.target.parent.addchild(event.target);
objectoriginalx3 = event.target.x;
objectoriginaly3 = event.target.y;
}

function dropobject3(event:mouseevent):void {
event.target.stopdrag();
var matchingtargetname:string = "target" + event.target.name;
var matchingtarget:displayobject = getchildbyname(matchingtargetname);
  if (event.target.droptarget != null && event.target.droptarget.parent == matchingtarget){
  event.target.removeeventlistener(mouseevent.mouse_down, pickupobject);
  event.target.removeeventlistener(mouseevent.mouse_up, dropobject);
  event.target.buttonmode = false;
  event.target.x = matchingtarget.x;
  event.target.y = matchingtarget.y;
 
  response_mc.gotoandstop(1);
  nextquestion.gotoandstop(1);
 
  count++;
  if (count==4){
   response_mc.gotoandstop(2);
   nextquestion.gotoandstop(2);
   nextquestion.addeventlistener(mouseevent.click, question3);
   function question3(event:mouseevent):void{
    gotoandstop(4);
    date.gotoandstop(2);
    authorq3.gotoandstop(2);
    titleq3.gotoandstop(2);
    publication.gotoandstop(2);
   
    response_mc.gotoandstop(1);
    nextquestion.gotoandstop(1);
   }
  }
 
 
} else {
  event.target.x = objectoriginalx3;
  event.target.y = objectoriginaly3;
  }

}

once try debug program. can line number error is. , trace objects in line, can find out null object.

 

for debug program, go debug -> debug movie -> in flash professional.

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