Maybe your Gtk2 install is broken, your code gives no such error at my machine (but ofcourse it doesn't show anything either. The following shows the list at my install.

use Gtk2 qw/-init/;
use Gtk2::SimpleList;

$main = Gtk2::Window->new('toplevel');
$list = Gtk2::SimpleList->new('test' => 'text',
    test2 => 'text');
$main->add($list);
$main->show_all;
Gtk2->main;
[download]

(that's with Gtk2, V1.122)