How to solve method error 401 ajax cascading dropdown?

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
[System.Web.Script.Services.ScriptService]

public class CasCadingDropDown : System.Web.Services.WebService
{
    //private DataSet ds = new DataSet();
    //private DataTable dt = new DataTable();
    public CasCadingDropDown()
    {

        //Uncomment the following line if using designed components 
        //InitializeComponent(); 
    }

    [WebMethod]
    public CascadingDropDownNameValue[] GetStates(string knownCategoryValues)
    {
        string query = "SELECT statename, stateid FROM tblstates";
        List<CascadingDropDownNameValue> states = GetData(query);
        return states.ToArray();
    }

    [WebMethod]
    public CascadingDropDownNameValue[] GetDistricts(int state)
    {
        //int state = Formats.ConvertToInt(CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues)["stateid"]);
        string query = string.Format("select districtname,districtid from tbldistricts where stateid={0}",state);
        List<CascadingDropDownNameValue> districts = GetData(query);
        return districts.ToArray();
    }
    private List<CascadingDropDownNameValue> GetData(string query)
    {
        
    string connstring = String.Format("Server=192.168.1.100;Port=5432;Encoding=UNICODE;User Id=postgres;Password=sggkishore;Database=SNCF;");
         NpgsqlCommand cmd = new NpgsqlCommand(query);
        List<CascadingDropDownNameValue> values = new List<CascadingDropDownNameValue>();
        using (NpgsqlConnection conn = new NpgsqlConnection(connstring))
        {
            conn.Open();
            cmd.Connection = conn;
            using (NpgsqlDataReader reader = cmd.ExecuteReader())
            {
                while (reader.Read())
                {
                    values.Add(new CascadingDropDownNameValue
                    {
                        name = reader[0].ToString(),
                        value = reader[1].ToString()
                    });
                }
                reader.Close();
                conn.Close();
                return values;
            }
        }
    }

<asp:DropDownList ID="ddlCState" runat="server" CssClass ="userentry" >
                                 <cc1:CascadingDropDown ID="cdlStates" TargetControlID="ddlCState" PromptText="Select State" 
                                  ServicePath="CascadingDropdown.asmx" ServiceMethod="GetStates"  runat="server" Category="StateId" />