Reloading swf inside a loader in Air for IOS

Hi friends,

Iam creating an elearning app.  i have 4 buttons on stage, when user clicks it will load 4 different lessons. I have created the following codes, its working fine. when i click same button again it is not loading the lesson. only one time i can click and load a lesson, 2nd time it is not loading.

Kindly help me to solve the issues..

import flash.events.MouseEvent;

import flash.display.Loader;

import flash.net.URLRequest;

import flash.system.LoaderContext;

import flash.system.ApplicationDomain;

var no_les:Number = 4;

var ldr: Loader = new Loader();

var req: URLRequest = new URLRequest();

var lc:LoaderContext = new LoaderContext(false, ApplicationDomain.currentDomain, null);

for (var inc1: Number = 1; inc1 <= no_les; inc1++) {

                this["bt" + inc1].addEventListener(MouseEvent.CLICK, menu_clicked);

}

function menu_clicked(event: MouseEvent) {

                ldr = new Loader();

                req.url = "app:/assets/lessons/les"+event.target.name.substr(2)+"/lmsframe.swf"

                ldr.load(req,lc);

                load_box.addChild(ldr);

}

close_but.addEventListener(MouseEvent.CLICK, close_clicked);

function close_clicked(event:MouseEvent){

                MovieClip(ldr.content).currentMovie.content_mc.gotoAndStop(1);      

                for(var inc2:Number = 0; inc2<=load_box.numChildren-1; inc2++){

                                load_box.removeChildAt(inc2);

                }

                ldr.unload();

}

Thanks in advance,

Regards,

Syed Abdul Rahim