Ajax dropdownlist Cascading error

[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 DropdownWebService : System.Web.Services.WebService {

    [WebMethod]
    public CascadingDropDownNameValue[] BindCountrydropdown(string knownCategoryValues, string category)
    {
        SqlConnection concountry = new SqlConnection(ConfigurationManager.ConnectionStrings["cnnstring"].ConnectionString);
        concountry.Open();
        SqlCommand cmdcountry = new SqlCommand("select * from Country", concountry);
        SqlDataAdapter dacountry = new SqlDataAdapter(cmdcountry);
        cmdcountry.ExecuteNonQuery();
        DataSet dscountry = new DataSet();
        dacountry.Fill(dscountry);
        concountry.Close();
        List<cascadingdropdownnamevalue> countrydetails = new List<cascadingdropdownnamevalue>();
        foreach (DataRow dtrow in dscountry.Tables[0].Rows)
        {
            string CountryID = dtrow["CountryID"].ToString();
            string CountryName = dtrow["CountryName"].ToString();
            countrydetails.Add(new CascadingDropDownNameValue(CountryName, CountryID));
        }
        return countrydetails.ToArray();
    }
    [WebMethod]
    public CascadingDropDownNameValue[] BindStatedropdown(string knownCategoryValues, string category)
    {
        int CountryID;
        StringDictionary countrydetails = AjaxControlToolkit.CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues);
        CountryID = Convert.ToInt32(countrydetails["Country"]);
        SqlConnection constate = new SqlConnection(ConfigurationManager.ConnectionStrings["cnnstring"].ConnectionString);
        constate.Open();
        SqlCommand cmdstate = new SqlCommand("select * from State where CountryID=@CountryID", constate);
        cmdstate.Parameters.AddWithValue("@CountryID", CountryID);
        cmdstate.ExecuteNonQuery();
        SqlDataAdapter dastate = new SqlDataAdapter(cmdstate);
        DataSet dsstate = new DataSet();
        dastate.Fill(dsstate);
        constate.Close();
        List<cascadingdropdownnamevalue> statedetails = new List<cascadingdropdownnamevalue>();
        foreach (DataRow dtstaterow in dsstate.Tables[0].Rows)
        {
            string stateID = dtstaterow["StateID"].ToString();
            string statename = dtstaterow["StateName"].ToString();
            statedetails.Add(new CascadingDropDownNameValue(statename, stateID));
        }
        return statedetails.ToArray();
    }
    [WebMethod]
    public CascadingDropDownNameValue[] BindRegiondropdown(string knownCategoryValues, string category)
    {
        int stateID;
        StringDictionary statedetails = AjaxControlToolkit.CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues);
        stateID = Convert.ToInt32(statedetails["State"]);
        SqlConnection conregion = new SqlConnection(ConfigurationManager.ConnectionStrings["cnnstring"].ConnectionString);
        conregion.Open();
        SqlCommand cmdregion = new SqlCommand("Select * from Region where StateID=@StateID", conregion);
        cmdregion.Parameters.AddWithValue("@StateID", stateID);
        cmdregion.ExecuteNonQuery();
        SqlDataAdapter daregion = new SqlDataAdapter(cmdregion);
        DataSet dsregion = new DataSet();
        daregion.Fill(dsregion);
        conregion.Close();
        List<cascadingdropdownnamevalue> regiondetails = new List<cascadingdropdownnamevalue>();
        foreach (DataRow dtregionrow in dsregion.Tables[0].Rows)
        {
            string regionID = dtregionrow["RegionID"].ToString();
            string regionname = dtregionrow["RegionName"].ToString();
            regiondetails.Add(new CascadingDropDownNameValue(regionname, regionID));

        }
        return regiondetails.ToArray();
    }
}