Webservice returning undefined

<script type="text/javascript" >

    $(function () {
        $.ajax({
            type: "POST",
            contentType: "application/json; charset=utf-8",
            url: 'WebServices/AutoComplete.asmx/GetCountries',
            data: "{}",
            datatype: "json",
            async: true,
            cache: true,
            success:
                function (data, event) {


                    $.map(data.d, function (item) {
                    //    alert(item);
                        //                        $("#<%= drpCountry.ClientID %>").index = item.countryid;
                        //                        $("#<%= drpCountry.ClientID %>").val = item.countryname;
                                      alert(item.countryname);

                        $("#<%= drpCountry.ClientID %>").append("<option value="+item.countryid+" >"+item.countryname+"</option>");

                    });
                }

        });

    });

                   </script>