Cannot access the stage/root method getChildByName

package lib.cms{
 
import lib.cms.MenuItem;
import flash.text.*;
import flash.display.*;
import flash.net.URLLoader;
import flash.net.URLRequest;
import caurina.transitions.*;
import com.utils.CallArg;
import flash.events.*;
 
	public class Menu {
		
		private var __menuList:XMLList;	 
		private var __loader:URLLoader;
		private var __xml:XML;
		
		var MenuStartX:Number = 100;
		var MenuStartY:Number = 100;
		var MenuItemPadding:Number = 5;
				
		public function Menu(XMLstr:String = "xml/mainmenu.xml"):void {
			trace("Menu class called. ");
			loadXML(XMLstr);
		}
 
		private function loadXML(XMLstr:String):void {
			__loader = new URLLoader();
			__loader.addEventListener(Event.COMPLETE, onXMLLoaded);
			__loader.load(new URLRequest(XMLstr));
		}
 
		private function onXMLLoaded(event:Event):void {
 
			// Put some error catching in case the XML is malformed.
			try {
				__xml = XML(event.target.data);
				__menuList = __xml.children();
				
				trace("XML menu loaded");
				
				for (var i:int =0; i<__menuList.length(); i++) {
					// for the first element there is no previous textfield inserted
					var title:String = __menuList[i].@title;
					var menu_text = __menuList[i].@text;
					var action:String = __menuList[i].attribute("action");
					if (i==0) {
						var _x = MenuStartX;
						var _y = MenuStartY;
						//createMainMenu(title, menu_text, action, _x , _y , i );
						//createSubmenus(__menuList,i);
					} else {
						// Create the text field getting positioning setting form the previous textField inserted
						var dx = getChildByName("MenuItem"+(i-1).toString()).x;
						var dy = getChildByName("MenuItem"+(i-1).toString()).y + 1180: Call to a possibly undefined method getChildByName.getChildByName("MenuItem"+(i-1).toString()).height + MenuItemPadding;
						//createMainMenu(title, menu_text, action, dx , dy , i );
						//createSubmenus(__menuList,i);
					}
				}
				
				
 
			} catch (error:Error) {
 
				// Display an error message.
				var errorMessage:TextField = new TextField();
				errorMessage.autoSize = TextFieldAutoSize.LEFT;
				errorMessage.textColor = 0xFF0000;
				errorMessage.text = error.message;
				this.stage.addChild(errorMessage);
				return;
			}
		}
 
	}
}