ASP.Net AJAX CascadingDropDown DropDownList - Method Error 500

hello,

I would like to populate Cascading DropDownList From SQL Server.

I prepare my project the same way as in this article:

http://www.aspsnippets.com/Articles/AJAX-Cascading-DropDown-Example-in-ASPNet.aspx

but all the time I have "Method error 500" I read many articles how to solve this issue but without success.

Below there are my codes:

----SQL DB has two tables:

1.tblUAP (UAP (PK), Start_Date,End_Date)

2.tblGAP(idGAP (PK),GAP,UAP(FK to tblUAP))

---project1.aspx

<%@ Page Language="C#"  EnableEventValidation="false" AutoEventWireup="true" CodeBehind="Project1.aspx.cs" Inherits="TEST.Project1" %>
 

<%@ Register assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" tagprefix="asp" %>


....

<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
            </asp:ToolkitScriptManager>
     
......  

 <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True">
                </asp:DropDownList>
               
                <asp:CascadingDropDown ID="DropDownList1_CascadingDropDown" runat="server" 
                    Category ="UAP"
                    TargetControlID="DropDownList1" 
                    PromptText ="-- Select UAP--"
                    LoadingText="[Searching UAP....] "
                    ServiceMethod="GetUAPs"
                    ServicePath ="Services.asmx">
                </asp:CascadingDropDown>

...



<asp:DropDownList ID="DropDownList2" runat="server">
                </asp:DropDownList>

                <asp:CascadingDropDown ID="DropDownList2_CascadingDropDown" runat="server" 
                    Category ="GAP"
                    TargetControlID="DropDownList2" 
                    PromptText ="-- Select GAP--"
                    LoadingText="[Searching GAP....] "
                    ServiceMethod="GetGAPs"
                    ServicePath ="Services.asmx"
                    ParentControlID="DropDownList1">
                </asp:CascadingDropDown>

----Services.asmx

using System;
using System.Web;
using System.Web.Services;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using AjaxControlToolkit;
using System.Collections.Generic;

namespace PDE
{
    /// <summary>
    /// Summary description for Services
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.Web.Script.Services.ScriptService]
    public class Services : System.Web.Services.WebService
    {

        [WebMethod]
        public CascadingDropDownNameValue[] GetUAPs(string knownCategoryValues)
        {
            string query = "SELECT UAP FROM tblUAP";
            List<CascadingDropDownNameValue> UAPs = GetData(query);
            return UAPs.ToArray();
        }

        [WebMethod]
        public CascadingDropDownNameValue[] GetGAPs(string knownCategoryValues)
        {
            string UAPs = CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues)["UAP"];
            string query = string.Format("SELECT GAP FROM tblGAP WHERE UAP = {0}", UAPs);
            List<CascadingDropDownNameValue> GAPs = GetData(query);
            return GAPs.ToArray();
        }


        private List<CascadingDropDownNameValue> GetData(string query)
        {
            string conString = ConfigurationManager.ConnectionStrings["Db_constr"].ConnectionString;
            SqlCommand cmd = new SqlCommand(query);
            List<CascadingDropDownNameValue> values = new List<CascadingDropDownNameValue>();
            using (SqlConnection con = new SqlConnection(conString))
            {
                con.Open();
                cmd.Connection = con;
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        values.Add(new CascadingDropDownNameValue
                        {
                            name = reader[0].ToString(),
                            value = reader[1].ToString()
                        });
                    }
                    reader.Close();
                    con.Close();
                    return values;
                }
            }
        }


    }
}

Please, could you give me advice what else Can I check ??

Br.