Javascript - Not Pushing To Array?

Trying to push some coordinates, as well as some stuff specified in a form by the user, to an an array called "seatsArray". Here's my code:

<div>
<img onLoad="shiftzoom.add(this,{showcoords:true,relativecoords:true,zoom:100});" id="image" src="plan1.bmp" width="1024" height="768">
</div>
<script type="text/javascript">
var seatsArray = [];
</script>
<br><input id="backnave" type="radio" name="area" value="backnave" /> Back Nave<br>
<input id="frontnave" type="radio" name="area" value="frontnave" /> Front nave<br>
<input id="middlenave" type="radio" name="area" value="middlenave" /> Middle nave<br>
<input type="radio" id="standardseat" name="seat" /><label for="radio1">Standard</label><br>
<input type="radio" id="wheelchairseat" name="seat" checked="checked" /><label for="radio2">Wheelchair</label><br>
<form id="my_form" action="savetext.aspx" method="post" onsubmit="return prepare()">
<input type="text" id="file_name" name="file_name" rows="1" cols="20" />
<input type="hidden" name="seatsArray" />
<input type="submit" value="Save" />
</form>
<form id="my_form" action="savetext.aspx" method="post" onsubmit="return prepare()">
<input type="text" id="file_name" name="file_name" rows="1" cols="20" />
<input type="hidden" name="seatsArray" />
<input type="submit" value="Save" />
</form>
<script type="text/javascript">
function prepare();
{
document.getElementById('seatsArray').value = seatsArray.join();
return true;
}
</script>
<script type="text/javascript">
var coordinates = document.getElementById("image");
coordinates.onclick = function(e) {
e = e || window.event;
if (e && e.pageX && e.pageX) {
e.posX = e.pageX;
e.posY = e.pageY;
} else if (e && e.clientX && e.clientY) {
var scr = {x:0,y:0},
object = e.srcElement || e.target;
//legendary get scrolled
for (;object.parentNode;object = object.parentNode) {
scr['x'] += object.scrollLeft;
scr['y'] += object.scrollTop;
}
e.posX = e.clientX + scr.x;
e.posY = e.clientY + scr.y;
}
var desc = "";
if(document.getElementByID("backnave").checked) {
desc = "BN, "+desc;
} else if(document.getElementByID("middlenave").checked) {
desc = "MN, "+desc;
} else if(document.getElementByID("frontnave").checked) {
desc = "FN, "+desc;
}
if(document.getElementById('wheelchairseat').checked) {
//Wheelchair seat is checked
desc = "Wheelchair "+desc;
}
seatsArray.push(desc + e.posX, e.posY);
}
</script>

But simply nothing is getting pushed to the array. I can tell this as I am using the following ASP.NET to write the array to a text file:

<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
string path = Server.MapPath(".")+"/"+Request.Form["file_name"] + ".txt";
if (!File.Exists(path))
{
using (StreamWriter sw = File.CreateText(path))
{
sw.WriteLine(Request.Form["seatsArray"]);
sw.WriteLine("");
}
}
using (StreamReader sr = File.OpenText(path))
{
string s = "";
while ((s = sr.ReadLine()) != null)
{
Response.Write(s);
}
}
}
</script>

The name of the text file is correct according to what the user put in the form "file_name". As you can see I made seatsArray a hidden form object so thats what the ASP.NET is trying to call.

Is something in the javascript in the wrong order or something? Because I just can't get it to fill up that text file.