Javascript issue

Hi,

I have used some js auto select code on a form that I have put together. It works fine when tested on a normal Html/PHP page but I am getting this error in WP from Firebug.

setting a property that has only a getter

from this line:

selectCtrl.options = null;

Has anyone got a solution? Here is the JS:

team = new Array(
new Array(
new Array("Male")
),
new Array(
new Array("Female")
),
new Array(
new Array("Male")
),
new Array(
new Array("Female")
)
);
function fillSelectFromArray(selectCtrl, itemArray, goodPrompt, badPrompt, defaultItem) {
var i, j;
var prompt;
for (i = selectCtrl.options.length; i >= 0; i--) {
selectCtrl.options = null;
}
prompt = (itemArray != null) ? goodPrompt : badPrompt;
if (prompt == null) {
j = 0;
}
else {
selectCtrl.options[0] = new Option(prompt);
j = 1;
}
if (itemArray != null) {
for (i = 0; i < itemArray.length; i++) {
selectCtrl.options[j] = new Option(itemArray[0]);
if (itemArray[1] != null) {
selectCtrl.options[j].value = itemArray[1];
}
j++;
}
selectCtrl.options[0].selected = true;
}
}

My Javascript is not verygood so any help would be appreciated. Thanks
Phil