No puedo aceder a una variable public

[asacura]

Buenas!
el problema es que kisiera editar una variable que tengo en una clase
accedo a esta mediante un getChildByName()
ya que la variable ke la creo se encarga de crear al resto de los npcs
el codigo es algo asi:

Código ActionScript:

for(var xgm:int=1; xgm <=100; xgm++){ trace('MDid_'+xgm); 
      if(vars['MDid_'+xgm]){ if(npc['tmpIdNpc_'+xgm]){ trace("No"); 
         _mainMap.getChildByName("npc_"+npc['tmpIdNpc_'+vars['MDid_'+xgm]]).pos_x = vars['MDcorx_'+xgm]; 
         _mainMap.getChildByName("npc_"+npc['tmpIdNpc_'+vars['MDid_'+xgm]]).pos_y = vars['MDcorx_'+xgm]; 
      }else{ trace("Si 2"); 
    _idNpc++; 
   var chuy:Npc = new Npc(vars['MDlifeb_'+xgm],vars['MDcorx_'+xgm],vars['MDcory_'+xgm],vars['MDname_'+xgm],1,1); 
   chuy.x = vars['MDcorx_'+xgm]; chuy.y = vars['MDcory_'+xgm]; chuy.name="npc_"+_idNpc; 
   npc['tmpIdNpc_'+vars['MDid_'+xgm]] = _idNpc; 
   _mainMap.addChild(chuy); 
   if(_idNpc==1){ _mainMap.addEventListener(Event.ENTER_FRAME, followInTheMap); } 
      } }else{ 
         xgm+=100; 
      } 
}
 

es el ke se encarga de crear los npc
y el archivo clase de npc es:

Código ActionScript:

package 
{ 
   import flash.display.MovieClip; 
   import flash.events.Event; 
   import flash.text.*; 
    
   public class Npc extends MovieClip 
   { 
      public var life:Number; 
      public var pos_x:Number; 
      public var pos_y:Number; 
      public var rute:Number; 
      public var iniRuteTime:Number; 
      public var _name:String; 
      public var _move:Number; 
      private var speed:Number = (55/20); 
      private var posRuteX:Number;  
      private var posRuteY:Number; 
      private var corx:Number; 
      private var cory:Number; 
      private var new_x:Number;  
      private var new_y:Number; 
      private var new_x2:Number;  
      private var new_y2:Number; 
      private var contenedor2:Number = 0; 
      private var contenedor:MovieClip = new MovieClip(); 
      private var name_txt:TextField = new TextField(); 
       
      public function Npc(fLife:Number,fPosx:Number,fPosy:Number,fName:String,finiRuteTime:Number,fmove:Number) 
      { 
         _move = fmove; 
         _name=fName; 
         life = fLife; 
         pos_x = fPosx; 
         pos_y = fPosy; 
         iniRuteTime = finiRuteTime; 
         rute = 1; 
         iniRuteTime = 0; 
         if(fName=="55GK-Kurck"){ contenedor = new tileSet1(); }else 
         if(fName=="39UC-Typhoon"){ contenedor = new tileSet3(); }else 
         if(fName=="78CQ-Imperia"){ contenedor = new tileSet4(); }else 
         if(fName=="98CR-Metamoft"){ contenedor = new tileSet6(); }else 
         { contenedor = new tileSet100_rutenium(); } 
            contenedor.x=-50; 
            contenedor.y=-50; 
            contenedor.stop(); 
         this.addChild(contenedor); 
         this.addEventListener(Event.ENTER_FRAME, actStatus); 
      } 
       
      private function actStatus(e:Event):void 
      { 
         this.x=this.pos_x; 
         this.y=this.pos_y; 
         if(contenedor2==0){ 
         name_txt.type=TextFieldType.DYNAMIC; 
         name_txt.text=_name; 
         name_txt.width=120; 
         name_txt.height=16; 
         name_txt.x=-60; 
         name_txt.y=50; 
         name_txt.selectable = false; 
         name_txt.textColor = 0x99FFFF; 
         name_txt.autoSize = TextFieldAutoSize.CENTER; 
         this.addChild(name_txt); 
         contenedor2++; 
         } 
         //Validamos ruta normal 
         if(rute == 1){ posRuteX=1000;posRuteY=1000; } 
         if(rute == 2){ posRuteX=2500;posRuteY=5000; } 
         if(rute == 3){ posRuteX=1700;posRuteY=200; } 
         if(rute == 4){ posRuteX=3080;posRuteY=2300; } 
         if(rute == 5){ posRuteX=4080;posRuteY=3500; } 
         if(rute == 6){ posRuteX=2050;posRuteY=4000; } 
         new_x = posRuteX-this.x; 
          new_y = posRuteY-this.y; 
          //Comprobamos que no se pase. 
          var absX:Number=Number(new_x.toString().split('-').join(''));var absY:Number=Number(new_y.toString().split('-').join('')); 
if(absX<=speed && absY<=speed){ if(rute!=6){rute++;}else{rute=1;} }else{ 
if(absX<=(speed*3) && absY>speed){if(new_x>=0){new_x2 = new_x+speed; }else{ new_x2=new_x-speed;}new_y2=new_y;/*trace(new_x+","+new_y);trace(new_x2+","+new_y2);*/}else  
if(absY<=(speed*3) && absX>speed){if(new_y>=0){new_y2=new_y+speed; }else{new_y2=new_y-speed; }new_x2 = new_x;/*trace(new_x+","+new_y);trace(new_x2+","+new_y2);*/}else{ 
new_x2=new_x;new_y2=new_y; 
} 
} 
if(new_x2>=0){ corx=speed; }else{ corx = 0-speed; } 
         if(new_y2>=0){ cory=speed; }else{ cory = 0-speed; } 
          
         if(corx < 0 && cory < 0){ this.contenedor.gotoAndStop('4'); } 
         if(corx >= 0 && cory < 0){ this.contenedor.gotoAndStop('3'); } 
         if(corx >= 0 && cory >= 0){ this.contenedor.gotoAndStop('2'); } 
         if(corx < 0 && cory >= 0){ this.contenedor.gotoAndStop('1'); } 
          
         this.x = this.x+corx; this.y= this.y+cory; 
         pos_x = this.x; pos_y = this.y; 
      } 
       
   } 
}
 

No se que estoy haciendo mal... por favor ayudenme : )
intento acceder a la variable pos_x y pos_y de esta forma
_mainMap.getChildByName("npc_"+npc['tmpIdNpc_'+vars['MDid_'+xgm]]).pos_x = vars['MDcorx_'+xgm];
_mainMap.getChildByName("npc_"+npc['tmpIdNpc_'+vars['MDid_'+xgm]]).pos_y = vars['MDcorx_'+xgm];
pero me da error