Hi, i am new to javascript and ive been working on some code for a few days and i desparately need some help. can someone please look at my code and tell me why i am getting the following error when viewing my file in IE?

I am getting the error:
Message: 'activeMenu.style' is null or not an object
Line: 101
Char: 4
Code: 0

The issues i see why when i view my code in IE is that for some reason i am getting a broken graphic on the comptuers tab but i checked the code and i dont see any reason why its doing that on only 1 tab, when the code is similar for all 6 objects.

The other issue i am experiencing is when i click on the text
<p>The best photo prints can now be made ... the sidemenu 6 appears. It is supposed to hide the activeMenu when the body is clicked on. any advice or points would be greatly appreciated. thank you in advance let me know if you need any other information
<html>
<head>
<link href="je.css" rel="stylesheet" type="text/css" />
<script type="text/JavaScript">
if(document.images){
image = new Array();
image[1]="main1.jpg";
image[2]="main2.jpg";
image[3]="main3.jpg";
image[4]="main4.jpg";
image[5]="main5.jpg";
image[6]="main6.jpg";
image[1].src="main1.jpg";
image[2].src="main2.jpg";
image[3].src="main3.jpg";
image[4].src="main4.jpg";
image[5].src="main5.jpg";
image[6].src="main6.jpg";
imageOver = new Array();
imageOver[1]="main1_over.jpg";
imageOver[2]="main2_over.jpg";
imageOver[3]="main3_over.jpg";
imageOver[4]="main4_over.jpg";
imageOver[5]="main5_over.jpg";
imageOver[6]="main6_over.jpg";
imageOver[1].src="main1_over.jpg";
imageOver[2].src="main2_over.jpg";
imageOver[3].src="main3_over.jpg";
imageOver[4].src="main4_over.jpg";
imageOver[5].src="main5_over.jpg";
imageOver[6].src="main6_over.jpg";
image[i] = new Image;
imageOver[i] = new Image;
image[i].src="main" + i + ".jpg";
imageOver[i].src="main" + i + "_over.jpg";
}
for (var i=1; i <=6; i++){
var maxZ=6; // this variable stores the z-index of the currently displayed menu in the tabbed menu system.
var activeMenu = null;
}
function swapIn(num){
if (document.images) document.images[num].src=imageOver[num].src;
}
function swapOut(num){
if (document.images) document.images[num].src=image[num].src;
}
function showMain(num){
maxZ++;
document.getElementById("mainMenu"+num).style.zIndex=maxZ;
}
function hideActive(){
activeMenu.style.left="10px";
}
function slideMenu(){
var x=xCoord();
if (x <= 126){
shiftMenu(2,0);
setTimeout("slideMenu()",10);
}
}

function startSlide(num){
if (activeMenu !==null)
hideActive();
activeMenu = document.getElementById("sideMenu"+num);
slideMenu();
;
}
</script>
<script type="text/JavaScript">
function xCoord() {
return parseInt(activeMenu.style.left);
}
function shiftMenu(dx, dy) {
xc=parseInt(activeMenu.style.left);
yc=parseInt(activeMenu.style.top);
activeMenu.style.left=xc+dx+"px";
activeMenu.style.top=yc+dy+"px";
}
</script>
</head>

<body >
<div id="logo" style="z-index: 2"><img src="logo.jpg" alt="" /></div>

<!-- Tabbed Menu Titles -->
<div class="mainTitles" id="mainTitle1" style="left: 10px; top: 28px">
<a href="JavaScript:showMain('1')"/>
<img src="main1.jpg" alt="Computers" onmouseover="swapIn(1)" onmouseout="swapOut(1)" />

</div>
<div class="mainTitles" id="mainTitle2" style="left: 104px; top: 28px">
<a href="JavaScript:showMain('2')">
<img src="main2.jpg" alt="Electronics" onmouseover="swapIn(1)" onmouseout="swapOut(1)" />
</a>
</div>
<div class="mainTitles" id="mainTitle3" style="left: 198px; top: 28px">
<a href="JavaScript:showMain('3')">
<img src="main3.jpg" alt="Accessories" onmouseover="swapIn(1)" onmouseout="swapOut(1)" />
</a>
</div>
<div class="mainTitles" id="mainTitle4" style="left: 292px; top: 28px">
<a href="JavaScript:showMain('4')">
<img src="main4.jpg" alt="Software" onmouseover="swapIn(1)" onmouseout="swapOut(1)" />
</a>
</div>
<div class="mainTitles" id="mainTitle5" style="left: 386px; top: 28px">
<a href="JavaScript:showMain('5')">
<img src="main5.jpg" alt="Services" onmouseover="swapIn(1)" onmouseout="swapOut(1)" />
</a>
</div>
<div class="mainTitles" id="mainTitle6" style="left: 480px; top: 28px">
<a href="JavaScript:showMain('6')">
<img src="main6.jpg" alt="Store" onmouseover="swapIn(1)" onmouseout="swapOut(1)" />
</a>
</div>


<!-- Tabbed Menu Contents -->
<div class="mainMenus" id="mainMenu1" = "style="z-index:-6">
<img src="mainmenu1.jpg" alt="" />
</div>
<div class="mainMenus" id="mainMenu2" = "style="z-index:-5">
<img src="mainmenu2.jpg" alt="" />
</div>
<div class="mainMenus" id="mainMenu3" = "style="z-index:-4">
<img src="mainmenu3.jpg" alt="" />
</div>
<div class="mainMenus" id="mainMenu4" = style="z-index:-3">
<img src="mainmenu4.jpg" alt="" />
</div>
<div class="mainMenus" id="mainMenu5" = style="z-index:-2">
<img src="mainmenu5.jpg" alt="" />
</div>
<div class="mainMenus" id="mainMenu6" = style="z-index:-1">
<img src="mainmenu6.jpg" alt="" />
</div>


<!-- Sliding Menu Contents -->
<div id="sideMenu" onClick="hideActive()">
<img src="sidemenu.jpg" alt="" usemap="#linkmap" />
</div>


<!-- Submenus of the Sliding Menu -->
<div id="sideMenu1" class="sideMenus" style="top: 130px; left: 10px">
<a href="JavaScript:startSlide('1')">
<img src="side1.jpg" alt="" />
</div>
</a>

<div id="sideMenu2" class="sideMenus" style="top: 160px; left: 10px">
<a href="JavaScript:startSlide('2')"/>
<img src="side2.jpg" alt="" />
</div>
<div id="sideMenu3" class="sideMenus" style="top: 190px; left: 10px">
<a href="JavaScript:startSlide('3')"/>
<img src="side3.jpg" alt="" />
</div>
<div id="sideMenu4" class="sideMenus" style="top: 222px; left: 10px">
<a href="JavaScript:startSlide('4')"/>
<img src="side4.jpg" alt="" />
</div>
<div id="sideMenu5" class="sideMenus" style="top: 252px; left: 10px">
<a href="JavaScript:startSlide('5')"/>
<img src="side5.jpg" alt="" />
</div>
<div id="sideMenu6" class="sideMenus" style="top: 282px; left: 10px">
<a href="JavaScript:startSlide('6')"/>
<img src="side6.jpg" alt=""/>
</div>

<!-- Sliding Menu Image Map -->
<map id="linkmap" name="linkmap">
<area shape="rect" coords="5,40,112,58"> <a href="JavaScript:startSlide('1')"/>
<area shape="rect" coords="5,70,112,88"> <a href="JavaScript:startSlide('2')"/>
<area shape="rect" coords="5,100,112,118"><a href="JavaScript:startSlide('3')"/>
<area shape="rect" coords="5,130,112,148"> <a href="JavaScript:startSlide('4')"/>
<area shape="rect" coords="5,160,112,178"> <a href="JavaScript:startSlide('5')"/>
<area shape="rect" coords="5,190,112,208"> <a href="JavaScript:startSlide('6')"/>
</map>



<!-- Page Content -->
<div id="main" onClick="hideActive()">
<h1>Printers</h1>
<img src="printer.jpg" alt="" />
<p>The best photo prints can now be made ... AT HOME. Introducing the Jackson
Electronics' <b>Picture Perfect</b> printer. Darkroom quality prints
without the cost, the mess, or the dark.</p>
<p>Photo Shopper calls JE's Picture Perfect "<i>the photo printer
we've been waiting for: high quality prints at an affordable price.</i>"
Photo Review gives it 5 stars, calling it <i>"the outstanding product
of the year."</i> As with all of our printers, make sure to choose JE's
archival quality paper and inks, which are guaranteed not to fade.
There is no better way to preserve your family memories than with
JE photo products.</p>
<p><a href="#">Order</a> the award-winning <b>Picture Perfect</b> printer
today for the special price of <b>$299.95</b> or choose one of the other many
fine printer products from Jackson Electronics.</p>
</div>

</body>
</html>