Microsoft JScript runtime error: Object doesn't support this property or method

response has an html for some user control.
i need to load a usercontrol in div.

Scenario is:
I have a 'type dropdownlist', based on selection made on type, i have to fill sub type dropdownlist.
onload of 'type ddl' i am calling a function to load subtype ddl.

View side code

<div>

<%=Resources.ProductLabels.Type%>

<%=Html.DropDownList("TypeDropDownList_1", Model.CustomPaxList, new { @class = "fldtls", onchange = "LoadPassengerSubTypes('1')" })%>
</div>

Javascript

function LoadPassengerSubTypes(controlPrefix) {
var proxy = new ServiceProxy({ show: true });
var selectedtype = 0;
//alert(("SubTypePaxControl_" + controlPrefix));
selectedtype = $("#TypeDropDownList_" + controlPrefix).val();
var serializeform = "selectedType=" + selectedtype + "&count=" + controlPrefix;
proxy.invoke(
'/Product/LoadSubTypePAXTypeControl/',
'GET',
serializeform,
function (response) {
$("#"+ controlPrefix ).html(response);
$("#"+ controlPrefix ).show();
});
return false;
}