我有一个Winform应用程序，我得到以下错误。你能帮我解决它吗？

public class ChangeLanguage
    {
        public void UpdateConfig(string key, string value)
        {
            var xmlDoc = new XmlDocument();
            xmlDoc.Load(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
            foreach (XmlElement xmlElement in xmlDoc.DocumentElement)
            {
                if (xmlElement.Name.Equals("appSettings"))
                {
                    foreach (XmlNode xNode in xmlElement.ChildNodes)
                    {
                        if (xNode.Attributes[0].Value.Equals(key))
                        {
                            xNode.Attributes[1].Value = value;
                        }
                    }
                }
            }
            ConfigurationManager.RefreshSection("appSettings");
            xmlDoc.Save(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
        }
    }
}