My ignorance of Ada will probably show through in this. When it comes down to it you're going to have a hard time finding some one with Ada experience and may be better off trying to contact the author of your examples or a similar tutorial (http://wiki.ada-dk.org/building_gui_with_glade_3
was what I found on the net).
You seem to have Gtk_New (Builder); twice in your code. Could this cause a conflict?
Wouldn't the Show_All need to be prefixed as Gtk.Widget.Show_All?
By the way the .glade file produced by libglade is becoming obsolete with a merge towards GtkBuilder. I'm also not too sure how glade files targeted at version 3 go with using in gtk2; probably ok in most cases else you'd hear more about it.