cannot append items in combobox using Gtk2 and glade

Select or download this

#!/usr/bin/perl
use strict;
use warnings;
...

$builder->get_object ('window1')->show_all;
Gtk2->main;

Select or download this

<?xml version="1.0"?>
<interface>
...
    </child>
  </object>
</interface>

Select or download this
Gtk-CRITICAL **: gtk_combo_box_append_text: assertion `GTK_IS_LIST_STORE (combo_box->priv->model)' failed at /home/abijr/progs/perl/gtk/hello line 22.

Select Code to Download