domain: g-io-error-quark / operation not supported / http request

[Marc Weber <marco-oweber gmx de>]

  unhandled exception (type Glib::Error) in signal handler:
  domain: g-io-error-quark
  code  : 15
  what  : Operation not supported

caused by this code:

    Glib::ustring xml_uri = Glib::ustring::compose("http://%1/media/feed/rss/%2";,
        prefs->getString("/options/ocalurl/str"), search_keywords);
    // If we are not UTF8
    if (!Glib::get_charset()) {
        xml_uri = Glib::filename_to_utf8(xml_uri);
    }

    // Open the RSS feed
    Glib::RefPtr<Gio::File> xml_file = Gio::File::create_for_uri(xml_uri);
#ifdef WIN32
    if (!xml_file->query_exists()) {
        widget_status->set_error(_("Could not connect to the Open Clip Art Library"));
        return;
    }
#endif
    xml_file->load_contents_async(
        sigc::bind<Glib::RefPtr<Gio::File> , Glib::ustring>(
            sigc::mem_fun(*this, &ImportDialog::on_xml_file_read),
                xml_file, xml_uri)
    );

The url which should be loaded is http://openclipart.org/media/feed/rss/car.

export GIO_EXTRA_MODULES= path to 

  libgiognomeproxy.la
  libgiognomeproxy.so
  libgiognutls.la
  libgiognutls.so
  libgiolibproxy.la
  libgiolibproxy.so

and that env var is read by glib on startup.

Do you see anything trivial I've been missing before I start diving into
all details to understand what's going wrong?

glib/glibmm/glib-networking version: 2.37.4

Marc Weber