protected configuration Deserialize(string filename)
        {
            XmlSerializer serializer = new XmlSerializer(typeof(configuration));
            serializer.UnknownNode += new
            XmlNodeEventHandler(serializer_UnknownNode);
            serializer.UnknownAttribute += new
            XmlAttributeEventHandler(serializer_UnknownAttribute);

            FileStream fs = new FileStream(filename, FileMode.Open);
            configuration webConfig;
            webConfig = (configuration)serializer.Deserialize(fs); // <-- ошибка тут
            fs.Close();
            return webConfig;
         }