C# App.Config ติดปัญหาเรื่องการอ่าน application config file ครับ

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="Domain" value="196.168.1.10"/>
    <add key="Databasename" value="RFIDsmartcard"/>
    <add key="Databaseusername" value="rfid"/>
    <add key="Databasepassword" value="rfid1234"/>
    <add key="Reader_comport" value="COM8"/>
  </appSettings>
</configuration>

using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Data.SqlClient;
using System.Configuration;



namespace Cafeteria_topup
{
    class Getdata
    {
        private static string database_config = "";
        private static Configuration getconfig = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);   
        public void Database()
        {
            database_config = "SERVER=" + getconfig.AppSettings.Settings["Domain"].Value + ";DATABASE=" + getconfig.AppSettings.Settings["Databasename"].Value + ";UID=" + getconfig.AppSettings.Settings["Databaseusername"].Value + ";PWD=" + getconfig.AppSettings.Settings["Databasepassword"].Value + ";";
            }

        }
    }
}