Slideshow loading in one frame, not loading in another

Question

I have two separate slideshows in my document. The slideshow on frame 1 uses  ixia_works.xml, the slideshow on frame 5 uses ixia_windows.xml.  wrote all of my slideshow code on frame 1 and created a variable to hold the xml file.  On frame 5 I assigned the new value of the variable. The slideshow on frame 1 works perfectly; the slideshow on frame 5 won't even load. Where did I go wrong?
Code on frame 1:
//in order to work with tweens, necessary to import tween classes
import fl.transitions.Tween;
import fl.transitions.TweenEvent;
import fl.transitions.easing.*;
stop();
//if it doesn't exist, make it, else unload it (coming from other frames)
if (!imgLoader) {
    var imgLoader:Loader;
} else {
    imgLoader.unload();
var fadeTween:Tween;
var xmlRequest:URLRequest = new URLRequest("ixia_works.xml");
var xmlLoader:URLLoader = new URLLoader(xmlRequest);
var imgData:XML;
var whichImg:String;
var imgNum:Number = 0;
var totalPics:Number;
var isFirst:Boolean = true;
var myTimer:Timer = new Timer(200);
//when xml is loaded, start timer, run the checker
function xmlLoaded(event:Event):void {
    myTimer.start();
    myTimer.addEventListener(TimerEvent.TIMER, checker);
    imgData = new XML(event.target.data);
//loads image
function showPic():void{
    myTimer.removeEventListener(TimerEvent.TIMER, checker);
    whichImg = imgData.image[imgNum].imgURL;
    totalPics = imgData.*.length();
    imgLoader = new Loader;
    imgLoader.load(new URLRequest(whichImg));
    slideShow_mc.addChild(imgLoader);
    fadeTween = new Tween(imgLoader, "alpha", None.easeNone, 0, 1, 2, true);
function checker(event:TimerEvent):void {
    if (imgNum == 0) {
        //if this is not the initial load, then you need to unload imgLoader
        if (!isFirst) imgLoader.unload();
        isFirst = false;
        showPic();
    } else if (imgNum < totalPics) {
        imgLoader.unload();
        showPic();
    } else {
        imgLoader.unload();
        imgNum = 0;
        showPic();
//when you click a button, go to the next/previous image
function clickHandler(event:MouseEvent):void {
    switch(event.target) {
        case next_btn:
            myTimer.addEventListener(TimerEvent.TIMER, checker);
            imgNum++;
            break;
        case prev_btn:
            imgNum--;
            myTimer.addEventListener(TimerEvent.TIMER, checker);
            break;
    if (imgNum == totalPics) {
        imgNum = 0;
    } else if (imgNum < 0) {
        imgNum = totalPics - 1;
    //determines menu state
    if (navBar_mc.currentLabel == "navIn") {
        navBar_mc.gotoAndStop("navOut");
    //make sure "our work" turns on
    wordWork_mc.alpha = 1;
//fades previous/next arrows in and out
function fadeArrow(event:MouseEvent):void {
    switch(event.target) {
        case prev_btn:
            arrowPrev_mc.play();
            break;
        case next_btn:
            arrowNext_mc.play();
            break;
    if (navBar_mc.currentLabel == "navHit") {
        navBar_mc.navActivate_mc.y = 0;
//menu functionality
function slideOut(event:MouseEvent):void {
    navBar_mc.gotoAndStop("navOut");   
//moves hit state of menu once invisible button is rolled over
function hitState(event:MouseEvent):void {
    if (navBar_mc.currentLabel == "navHit") {
        navBar_mc.navActivate_mc.y = 0;
//put this here to ensure the commands get executed
hitState_btn.addEventListener(MouseEvent.MOUSE_OVER, hitState);
hitState_btn.useHandCursor = false;
xmlLoader.addEventListener(Event.COMPLETE, xmlLoaded);
next_btn.addEventListener(MouseEvent.CLICK, clickHandler);
prev_btn.addEventListener(MouseEvent.CLICK, clickHandler);
next_btn.addEventListener(MouseEvent.MOUSE_OVER, fadeArrow);
prev_btn.addEventListener(MouseEvent.MOUSE_OVER, fadeArrow);
navBar_mc.addEventListener(MouseEvent.CLICK, slideOut);
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
code on frame 5:
stop();
xmlRequest = new URLRequest("ixia_windows.xml");

Answer 1

Hmm. That's a very good question. It is loading the first slideshow.
Well, after seeing your question, I replaced the lines on frame 1:
var xmlRequest:URLRequest = new URLRequest("ixia_works.xml");
var xmlLoader:URLLoader = new URLLoader(xmlRequest);
with the following:
var xmlLoader:URLLoader = new URLLoader();
      xmlLoader.load(new URLRequest("ixia_works.xml"));
and on frame 5 replaced the code with the following:
xmlLoader.load(new URLRequest("ixia_windows.xml"));
and now I get the following error messages on frame 5:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at experiment_fla::MainTimeline/showPic()
    at experiment_fla::MainTimeline/checker()
    at flash.utils::Timer/_timerDispatch()
    at flash.utils::Timer/tick()
And still no loading on frame 5.