Ошибка error not a table

I need help with an ajax call I am performing, I am passing back an array from the backend as seen below, if I alert the data on the front end I get this.

However when I pass it through, google charts tells me it’s not an array.

Uncaught Error: Not an array
    at gvjs_oba (format+en_GB,default+en_GB,ui+en_GB,corechart+en_GB.I.js:272)
    at new gvjs_Pl (format+en_GB,default+en_GB,ui+en_GB,corechart+en_GB.I.js:274)
    at drawChart (Default.aspx:60)
    at Object.success (Default.aspx:43)
    at j (jquery-1.11.1.min.js:2)
    at Object.fireWith [as resolveWith] (jquery-1.11.1.min.js:2)
    at x (jquery-1.11.1.min.js:4)
    at b (jquery-1.11.1.min.js:4)
    at Object.send (jquery-1.11.1.min.js:4)
    at Function.ajax (jquery-1.11.1.min.js:4)

Ajax Query

<script lang="javascript">

        var chart_data;
        var startdate = "default";
        var enddate = "default";
        google.load("visualization", "1", {packages:["corechart"]});
        google.setOnLoadCallback(load_page_data);

        function load_page_data()
        {
            $.ajax({
                type: "post",
                url: 'feed.aspx/GetJsonwithStringBuilder',
                data: JSON.stringify({y: $('input[name=yaxis]:checked').val()}),
                contentType: "application/json; charset=utf-8",
                dataType: "text",
                async: false,
                success: function (data) {
                    if (data) {
                    drawChart(data, "My Chart", "Members");
                    }

                },
                error: function () {
                    alert('error');
                }
        });
        }

        function drawChart(chart_data, chart1_main_title, chart1_vaxis_title) {
            var chart1_data = new google.visualization.arrayToDataTable(chart_data);
            var chart1_options = {
                title: chart1_main_title,
                hAxis: { title: 'Month', type: 'string' },
                seriesType: 'bars',
                vAxis: { title: chart1_vaxis_title, titleTextStyle: { color: 'red' } }
            };

            var chart1_chart = new google.visualization.ComboChart(document.getElementById('chart_div'));
            chart1_chart.draw(chart1_data, chart1_options);
        }
        </script>

This is the backend

 [WebMethod()]
[ScriptMethod(ResponseFormat = ResponseFormat.Json)]
public static string GetJsonwithStringBuilder(string y)
{
    DataTable dsChartData = new DataTable();
    StringBuilder strScript = new StringBuilder();

    try
    {
        dsChartData = GetChartData();

        strScript.Append("[[");

        foreach (DataColumn column in dsChartData.Columns)
        {
            strScript.Append(""" + column.ColumnName + "",");
        }

        strScript.Remove(strScript.Length - 1, 1);
        strScript.Append("],");

        foreach (DataRow row in dsChartData.Rows)
        {
            strScript.Append("[");
            foreach (DataColumn column in dsChartData.Columns)
                if (column.ColumnName == "Month")
                    strScript.Append(""" + CultureInfo.CurrentCulture.DateTimeFormat.GetAbbreviatedMonthName(Int32.Parse(row[column.ColumnName].ToString())) + "",");
                else if (IsNumber(row[column.ColumnName].ToString()))
                    strScript.Append("" + row[column.ColumnName] + ",");
                else
                    strScript.Append(""" + row[column.ColumnName] + "",");

            strScript.Remove(strScript.Length - 1, 1);
            strScript.Append("],");
        }

        strScript.Remove(strScript.Length - 1, 1);
        strScript.Append("]");
        return strScript.ToString();
    }
    catch (Exception ex)
    {

    }
    finally
    {
        dsChartData.Dispose();
        strScript.Clear();
    }

    return "";
}

You need to use data.d instead of data in success function

$.ajax({
     type: "post",
     url: 'feed.aspx/GetJsonwithStringBuilder',
     data: JSON.stringify({y: $('input[name=yaxis]:checked').val()}),
     contentType: "application/json; charset=utf-8",
     dataType: "json",
     async: false,
     success: function (data) {
          var dataObj=JSON.parse(data.d);
          if (dataObj) {
             drawChart(dataObj, "My Chart", "Members");
          }
      },
      error: function () {
         alert('error');
      }
});