[Solved] Populate ASP.Net ListBox using jQuery AJAX Error: 500 Internal Server Error

Behind I send a question that I posted for a few minutes ago but it is not correct so.

I get a website completly if I delete this two rows in the ajax code contentType: "application/json; charset=utf-8", dataType: "json",

If I keep it the script doesn't work. There is 500 Internal Server Error.

Can someone help me to fix it?

Hello, 

I try to populate the ListBox, but the ajax part get me the website completely and not the List Item only.

Here is the code:

HTML

<asp:ListBox runat="server" ID="ListBoxSHIPTO" OnSelectedIndexChanged="ListBoxSHIPTO_SelectedIndexChanged"
    Rows="10"></asp:ListBox>
<script type="text/javascript">
    $(document).ready(function () {
        $('#MainContent_TextBoxSHIPTO').keyup(function () {
            search_val = $(this).val(); //console.log(search_val);
            if (search_val.length > 0) {
                $.ajax({
                    url: '/Rule.aspx/GetCustomers',
                    type: "POST",
                    contentType: "application/json; charset=utf-8",
                    dataType: "json",
                    data: { searchTerm: search_val },
                    success: function (r) {
                        var lstCustomers = $("#MainContent_ListBoxSHIPTO");
                        lstCustomers.empty();
                        $.each(r.d, function () {
                            lstCustomers.append($("<option></option>").val(this['Value']).html(this['Text']));
                            console.log(this['Wert']);
                        });
                        $('#MainContent_PanelSHIPTO').show();
                        var CusInput = $('#MainContent_TextBoxSHIPTO').position();
                        $('#MainContent_PanelSHIPTO').css({ top: CusInput.top + 17, left: CusInput.left });
                    },
                    error: function (error) {
                        alert(error);
                    }
                });
            }
            else {
                $('#MainContent_PanelSHIPTO').hide();
            }
        })
    });
</script>

C#

[System.Web.Services.WebMethod]
public static List<ListItem> GetCustomers(string searchTerm)
{
    List<ListItem> items = new List<ListItem>();
    string query = "SELECT Top 30 [CUSTOMER] AS Wert " + ",[CUSTOMER] + ' - ' + CASE WHEN [NAME] = '' OR [NAME] IS NULL THEN 'not found' ELSE [NAME] END AS Titel " + "FROM [Admin].[t_customer] " + "WHERE CASE WHEN @customer <> '' OR @customer IS NOT NULL THEN " + " CASE WHEN [CUSTOMER] like '%' + @customer + '%' OR [NAME] like '%' + @customer + '%' THEN 1 ELSE 0 END " + " ELSE 1 " + " END = 1 " + "ORDER BY [CUSTOMER]";
    SqlConnection con = new SqlConnection();
    SqlCommand cmd = new SqlCommand();
    con.ConnectionString = ConfigurationManager.ConnectionStrings["CPR_ConnNewCPR"].ConnectionString;
    cmd.CommandText = query;
    cmd.Parameters.AddWithValue("@customer", !string.IsNullOrEmpty(searchTerm) ? searchTerm : (object)DBNull.Value);
    cmd.Connection = con; con.Open();
    SqlDataReader sdr = cmd.ExecuteReader();
    while (sdr.Read())
    {
        items.Add(new ListItem
        {
            Value = sdr["Wert"].ToString(),
            Text = sdr["Titel"].ToString()
        });
    }
    sdr.Close();
    cmd.Dispose();
    con.Close();
    return items;
}

Can you help me the fix the errhor?

Thank you in advance Best regards

Iryna