C# - Disable Or Enable 2nd Dropdownlist In Aspx Based On Selected Choice Of The 1st Dropdownlist Box

I am having a problem with disabling DropDownList based on the chice of 1st DropDownList, there is no post back occuring, and it is a template based web app here is the current code:

<script type="text/javascript">
$(function() { var dropDownList1 = $('#<%= ddlUserType.ClientID %>');
var dropDownList2 = $('#<%= ddlMember.ClientID %>'); dropDownList1.change(function(e) {
if ( jQuery("#ddlUserType").val() != "ETOC") dropDownList2.removeAttr('disabled'); e.preventDefault();
else
dropDownList2.removeAttr('enabled'); e.preventDefault(); }
} );
</script>

what is happening now is page is blank and if I remove the above code everything shows, where I am going wrong. here is the plain and final javascript code which worked:

<script language="javascript">
function CheckDropDownState(lstbox)
{
if (lstbox.selectedIndex == 3) { document.forms[0].ddlMember.disabled = 1; }
else { document.forms[0].ddlMember.disabled = 0; }
}
</script>

and thew .aspx code: <asp:dropdownlist id="ddlUserType" runat="server" onclick="CheckDropDownState(this);"></asp:dropdownlist>