jquery.dataTables.min.js: Uncaught TypeError: Cannot read property 'length' of undefined

'''[WebMethod(EnableSession = true)]
[ScriptMethod(ResponseFormat = ResponseFormat.Json, UseHttpGet = true)]
public string GetTableData()
{
var echo = int.Parse(HttpContext.Current.Request.Params["sEcho"]);
var displayLength = int.Parse(HttpContext.Current.Request.Params["iDisplayLength"]);
var displayStart = int.Parse(HttpContext.Current.Request.Params["iDisplayStart"]);
var sortOrder = HttpContext.Current.Request.Params["sSortDir_0"].ToString(CultureInfo.CurrentCulture);
var roleId = HttpContext.Current.Request.Params["roleId"].ToString(CultureInfo.CurrentCulture);

        var records = GetRecordsFromDatabaseWithFilter().ToList();
        if (!records.Any())
        {
            return string.Empty;
        }

        var orderedResults = sortOrder == "asc"
                             ? records.OrderBy(o => o.ReqNo)
                             : records.OrderByDescending(o => o.ReqNo);
        var itemsToSkip = displayStart == 0
                          ? 0
                          : displayStart + 1;
        var pagedResults = orderedResults.Skip(itemsToSkip).Take(displayLength).ToList();
        var hasMoreRecords = false;

        var sb = new StringBuilder();
        sb.Append(@"{" + "\"sEcho\": " + echo + ",");
        sb.Append("\"recordsTotal\": " + records.Count + ",");
        sb.Append("\"recordsFiltered\": " + records.Count + ",");
        sb.Append("\"iTotalRecords\": " + records.Count + ",");
        sb.Append("\"iTotalDisplayRecords\": " + records.Count + ",");
        sb.Append("\"aaData\": [");
        foreach (var result in pagedResults)
        {
            if (hasMoreRecords)
            {
                sb.Append(",");
            }

            sb.Append("[");
            sb.Append("\"" + result.Id + "\",");
            sb.Append("\"" + result.ReqName + "\"");                             
            sb.Append("]");
            hasMoreRecords = true;
        }
        sb.Append("]}");
        return sb.ToString();
    }

    private static IEnumerable<tbl_Ticket> GetRecordsFromDatabaseWithFilter()
    {
        HajtRequestDataContext dataContext = new HajtRequestDataContext();
        //var RequestList = 
        //return RequestList.ToList();
        List<tbl_Ticket> mylist = new List<tbl_Ticket>();


        var test = (from e in dataContext.tbl_Tickets
                    select e).ToList();
        mylist = test;
        return mylist;

    }

$(document).ready(function () { $.ajaxSetup({ cache: false }); var table = $('#tblData').DataTable({ "filter": false, "pagingType": "simple_numbers", "orderClasses": false, "order": [[0, "asc"]], "info": false, "scrollY": "450px", "scrollCollapse": true, "bProcessing": true, "bServerSide": true, "url": "data.json", "dataSrc": "aoData", "sAjaxSource": "WebService.asmx/GetTableData", "fnServerData": function (sSource, aoData, fnCallback) { aoData.push({ "name": "roleId", "value": "admin" }); alert(sSource); $.ajax({ "dataType": 'json', "contentType": "application/json; charset=utf-8", "type": "GET", "url": sSource, "data": aoData, "success": function (msg) { var json = jQuery.parseJSON(msg.d); alert(msg.d); fnCallback(msg.d); $("#tblData").show(); }, error: function (xhr, textStatus, error) { if (typeof console == "object") { console.log(xhr.status + "," + xhr.responseText + "," + textStatus + "," + error); } } }); }, fnDrawCallback: function () { $('.image-details').bind("click", showDetails); } }); })

<div class="row">
    <div class="col-xs-12">

        <div class="box">
            <div class="box-header">
                <h3 class="box-title">All Admin Request List</h3>
            </div>
            <!-- /.box-header -->
            <div class="box-body">

                <table id="tblData" class="table table-bordered table-striped">
                    <thead>
                        <tr>
                            <th>Id</th>
                            <th>ReqName</th>
                        </tr>
                    </thead>
                    <tbody></tbody>

                </table>
            </div>
        </div>
    </div>