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I am trying to create a standard starter program for developping Ada programs with use of Gtk.
I copied this program from some example program. but I do get a problem with as the program does create a NULL pointer to a widget. That happens in connection with Glade 3 and the GTk builder (Gtk version 2.24

The program is:

procedure Algemeen is
Builder : Gtkada_Builder;
Error : Glib.Error.GError;
answer : Message_Dialog_Buttons := Button_OK;
Widge : Gtk_Widget;

begin
Gtk.Main.Init;
Gtk_New (Builder);
Error := Add_From_File (Builder, "algemeen.glade");
if Error /= null then
answer := Message_Dialog( Msg => "Error : " & Get_Message (Error),
Buttons => Button_OK,
Title => "Error");
Error_Free (Error);
return;
end if;
Gtk_New (Builder);
Register_Handler
(Builder => Builder,
Handler_Name => "Main_Quit", -- from XML file <signal handler=..>
Handler => Algemeen_Callbacks.On_Window_Destroy'Access);
Do_Connect (Builder);
-- Find our main window, then display it and all of its children.
Widge := Get_Widget (Builder, "algemeen_window"); Widge gets a Null pointer as value
Show_All (Widge); with a Nullpointer Show_All crashes
etc. etc.

The value of Builder looks a coorect value as I can by stepping through the code see the correct buildup of the window.
The name of the mainwindow "algemeen_window" corresponds with the name of the toplevel window in Glade 3

Is there anyone who can tell me what I do wrong or who can Show me a clesr explanation of the way I should use the conversion from a Glade file in my program

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.

Thanks, yes the second time GtkNew was the problem. Sometimes you need somebody who looks with a fresh eye, because when you are well into tour work you are blind for such faults.