Error #2007: Parameter listener must be non-null.

Question

I got this error in a for loop:
for (var i=0; i<=4; i++)
var titleLength:int = sensors[i].name.indexOf("S");
var title:String = sensors[i].name.slice(0,titleLength);
trace(title);                                                            //test;
sensors[i].addEventListener(MouseEvent.CLICK,s_thClick);
function s_thClick(event:MouseEvent):void
  trace(event.currentTarget.name);                            //shows the right name
  event.currentTarget.removeEventListener(MouseEvent.MOUSE_OUT, ("f_"+title+"Go") as Function);
  event.currentTarget.removeEventListener(MouseEvent.MOUSE_OVER, ("f_"+title+"Display")as Function );
the second trace() in this code shows exactly what I wanted but a 2007 error occurs at the line of the code.
Can someone help me figure this out?

Answer 1

I mean get that function out of the loop altogether... there can only be one function, where the variables used remain as variables, so when you start using it, the value of "i" at that time will be 5 (where the loop ended).  It does not remember a specific value of i for each object you ran thru the loop.
for (var i=0; i<=4; i++)
   sensors[i].addEventListener(MouseEvent.CLICK,s_thClick);
function s_thClick(event:MouseEvent):void
   var sensor = event.currentTarget; // might need to be... = MovieClip(event.currentTarget)
   var titleLength:int = sensor.name.indexOf("S");
   var title:String = sensor.name.slice(0,titleLength);
  sensor.removeEventListener(MouseEvent.MOUSE_OUT, ("f_"+title+"Go") as Function);
  sensor.removeEventListener(MouseEvent.MOUSE_OVER, ("f_"+title+"Display")as Function );
  switch (sensor)
   case homeS :
    break;
   case portS :
    maskParent2.portMsk.scaleY = -20;
    break;
   case contactS :
    maskParent2.contactMsk.scaleY = -20;
    break;
   case galleryS:
    maskParent.galleryMsk.scaleY = -20;
       break;
   case resumeS:
       maskParent.resumeMsk.scaleY=-20;
    break;
   default :
    break;
  sensor.y = -544;
  MovieClip(title + "Btn").gotoAndStop("show"+title);