Select Menu Customer - Expected Error

I'm still having problems with a Javascript 'Lookup' function. Basically, I have a select menu 'Customer' which triggers a 3 JS functions, to populate 2 extra select menus.

Code:
<script type="text/javascript" language="javascript">
$(document).ready(function(){
$('#customer').change(function() {
var option=$(this).val();
getCustContact(this);
getCostCentreContact(this);
$.get('getCostCentre.php',{select:option},function(data){
$('#result').html(data).hide().fadeIn(1000); .....

Using IE Developer Tools, during debugging, I get this error:
Expected ';' Error

This relates to either:
Code:
eval(ajax_CustContact[index].response);
or
Code:
eval(ajax_CostCentreContact[index].response);
(it's a bit random, as sometimes it works, sometimes it doesn't)

I have tried changing the 'custid' to 'custname' to check whether it was an integer causing the problem, but had the same problem.