Getting menu after glade2->gtkbuilder-convert-> what then?

[Igor Gorbounov <igorbounov topazelectro ru>]

Hi, All,
I urgently need an explanation or example on how a menuitem
can be got in a program after creating a glade2 file, converting
it to gtkbuilder file, then loading it ia a program and then...

Mainwindow::Mainwindow(BaseObjectType* cobject, const 
Glib::RefPtr<Gtk::Builder>& refBuilder)
: Gtk::Window(cobject)
{
   refXml = refBuilder;
   // that works fine with Gtk::Entry *measured_t_entry:
   refXml->get_widget("measured_t_entry", measured_t_entry);
   // that doesn't compile with Gtk::Action *menu_exit:
   refXml->get_widget("menu_exit", menu_exit);
   // that doesn't work with Gtk::Action *menu_exit in runtime:
   refXml->get_object("menu_exit");
...
   menu_exit->signal_activate().connect(sigc::mem_fun(*this, 
&Mainwindow::on_menu_exit_activate));
}

The error message is: Gtk-CRITICAL **: gtk_text_buffer_emit_insert: 
assertion `g_utf8_validate (text, len, NULL)' failed

Any help needed.
   Igor Gorbounov