Method Error 500 on cascading dropdownlist

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.Web.Script.Services.ScriptService]
public class ServiceCS : System.Web.Services.WebService
{
[WebMethod]
public CascadingDropDownNameValue[] GetCountries(string knownCategoryValues)
{
string query = "SELECT DISTINCT Country FROM Customers";
List<cascadingdropdownnamevalue> countries = GetData(query);
return countries.ToArray();
}

[WebMethod]
public CascadingDropDownNameValue[] GetCities(string knownCategoryValues)
{
string country = CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues)["Country"];
string query = string.Format("SELECT DISTINCT City FROM Customers WHERE Country = '{0}'", country);
List<cascadingdropdownnamevalue> cities = GetData(query);
return cities.ToArray();
}

[WebMethod]
public CascadingDropDownNameValue[] GetVillages(string knownCategoryValues)
{
string cities= CascadingDropDown.ParseKnownCategoryValuesString(knownCategoryValues)["City "];
string query = string.Format("SELECT DISTINCT village FROM Customers WHERE City = '{0}'", cities);
List<cascadingdropdownnamevalue> vilgs = GetData(query);
return vilgs.ToArray();
}

private List<cascadingdropdownnamevalue> GetData(string query)
{
string conString = ConfigurationManager.ConnectionStrings["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[0].ToString()
});
}
reader.Close();
con.Close();
return values;
}
}
}
}