Unable to disable a drop down list after ajax call returns

[ISSI]

I am inserting a drop down list(\[code\]<select>\[/code\]) inside a \[code\]<div>\[/code\] using innerHTML=xmlhttp.responseTextAfter this drop down list is inserted I am trying to disable this list using In HTML\[code\]<select id="mySelect" onChange="display_data(this.value);"> <option>Vehicle Make</option></select><div id="products_model" style="padding-top:5px"><select id="mySelect1" disabled> <option>Vehicle Model</option></select><div>\[/code\]In JS\[code\]display_data(){ xmlhttp=GetXmlHttpObject(); var url="indexajax.php"; url=url+"?manufacturers_id="+manufacturers_id; xmlhttp.onreadystatechange=function() { if (xmlhttp.readyState==4 || xmlhttp.readyState=="complete") { document.getElementById('products_model').innerHTML=xmlhttp.responseText; } } xmlhttp.open("GET",url,true); xmlhttp.send(null); var z=document.getElementById("mySelect"); var x=document.getElementById("mySelect1"); var strUser1 = z.options[z.selectedIndex].value; if (strUser1 == "Vehicle Make") x.disabled = true;}\[/code\]indexajax.php\[code\]<select id="mySelect1"onchange="display_datamodel('<?=$manufacturers_id?>',this.value);" > <option>Vehicle Model</option>........<some php logic to enter options>....</select><div id="productsnamemodel" style="padding-top:5px"><select id="mySelect2" onChange="display_data(this.value);" disabled> <option>Vehicle Series</option></select><div>\[/code\]This is not working. Is it because this HTML element was dynamically inserted in the DOM.If is it show is there any workaround of doing this.For some reason I can not make this drop down list disabled in AJAX response itself. Its a cascading drop down list in which I wan to disable second dropdown if first one was set to default.