how to solve json and web service error , return null message !

See more:

ASP.NET

JSONP

webservice

i have aproblem when display my page with json return null in alert message , webservice return my normal data , but not display on page

web service (DirectoryService.asmx)

Public Class GetDirectory
     Inherits System.Web.Services.WebService

    <WebMethod()> _
    Public Function LoadData() As String
        'List(Of Directory)()
        System.Threading.Thread.Sleep(500)
        Dim da As New Directories()
        Dim dt As New Directories.DirectoriesDataTable
        dt = da.Read("3", Nothing, 1, 5)

        Dim serializer As New System.Web.Script.Serialization.JavaScriptSerializer()
        Dim rows As New List(Of Dictionary(Of String, Object))()
        Dim row As Dictionary(Of String, Object)

        For Each dr As DataRow In dt.Rows
            row = New Dictionary(Of String, Object)()

            For Each col As DataColumn In dt.Columns
                row.Add(col.ColumnName, dr(col))
            Next

            rows.Add(row)
        Next

        Return serializer.Serialize(rows)

    End Function

* web service result

<string xmlns="http://tempuri.org/">
[{"DirectoryID":1,"DirectoryName":"artist","DirectoryNameAr":"الفنانون","DirectoryImage":"41570.7052485995.jpg","AllowDisplay":true,"OrderBy":2,"CreatedOn":"\/Date(1382536533483)\/"},{"DirectoryID":2,"DirectoryName":"Developer","DirectoryNameAr":"المطورون","DirectoryImage":"41571.6455421065.jpg","AllowDisplay":true,"OrderBy":1,"CreatedOn":"\/Date(1382617774857)\/"},{"DirectoryID":3,"DirectoryName":"Teachers","DirectoryNameAr":"المعلمين","DirectoryImage":"123123","AllowDisplay":true,"OrderBy":3,"CreatedOn":null},{"DirectoryID":4,"DirectoryName":"face","DirectoryNameAr":"الفنانون","DirectoryImage":"41570.7052485995.jpg","AllowDisplay":true,"OrderBy":2,"CreatedOn":"\/Date(1382536533483)\/"},{"DirectoryID":5,"DirectoryName":"nesho","DirectoryNameAr":"المطورون","DirectoryImage":"41571.6455421065.jpg","AllowDisplay":true,"OrderBy":1,"CreatedOn":"\/Date(1382617774857)\/"}]
</string>

* Json on my page (Loading.aspx)

<script src="js/jquery-1.6.4.min.js"></script>
        <script type="text/javascript">
            var skiprows = 1;
            $(document).ready(function () {
                fnBuildData();
                $("#btnComments").bind("click", function () {
                    fnBuildData();
                    return false;
                })
            });

            //$(window).scroll(function () {
            //    if ($(window).scrollTop() == $(document).height() - $(window).height()) {

            //        fnBuildData();
            //    }
            //});
            function fnBuildData() {

                $("#imgLoading").show();
                $.ajax({
                    type: "POST",
                    contentType: "Application/json ; charset=utf-8",
                    url: "GetDirectory.asmx/LoadData",
                    data: '{}',
                    datatype: "json",
                    success: function (msg) {

                        var nextrows = <%= getrows%> +1;
                    skiprows += nextrows;

                    var cmntobject = $.parseJSON(msg.d);
                    alert(cmntobject);
                    $("#imgLoading").hide();
                    if (cmntobject.length < nextrows)
                    { $("#btnComments").hide(); }
                    $.each(cmntobject, function (index, cmnt) {
                        $("#resultsTable").append("<table><tr><td>DirectoryName :</td><td>"
                            + cmnt.DirectoryName + "</td></tr><tr><td> DirectoryNameAr : </td><td> "
                            + cmnt.DirectoryNameAr + "</td></tr><tr><td colspan='2' nowrap='nowrap'>"
                            + cmnt.DirectoryID + "<hr /></td></tr></table>");
                    });

                }
                    ,
                error: function () { alert('Error occured , try later .'); $("#imgLoading").hide(); }
            });
            }


   </script>

* asp

<div id="resultsTable">

</div>
<img id="imgLoading" alt="loading" src="images/loadingAnimation.gif" />
<asp:ImageButton ID="btnComments" EnableViewState="false" Width="90" Height="90" ClientIDMode="Static" runat="server" ImageUrl="~/images/loadmore.jpg" />





when display my page (loading.aspx) but it return message (null)



where is my problem ?