Пол-часа уже парюсь, просто проклятье какое-то: The root element is missing. В чем я не прав?

        XmlSerializer xs = new XmlSerializer(responce.GetType());
        System.IO.Stream mStream = new System.IO.MemoryStream();
        xs.Serialize(mStream, responce);

        XmlDocument xmlResponce = new XmlDocument();
        
        try
        {
            xmlResponce.Load(mStream);
        }
        catch (XmlException ex)
        {
            throw new SoapException(ex.Message, XmlQualifiedName.Empty);
        }