m_WhatsApp.Connect();

            string datFile = getDatFileName("4917676232390");
            byte[] nextChallenge = null;
            if (File.Exists(datFile))
            {
                try
                {
                    string foo = File.ReadAllText(datFile);
                    nextChallenge = Convert.FromBase64String(foo);
                }
                catch (Exception) { };
            }
            else
            {
                nextChallenge = Convert.FromBase64String("");
            }

            m_WhatsApp.Login(nextChallenge);