Firebug shows 500?

gistfile1.aw

<?php

namespace Yela;

class PageNotFoundException
    extends Exception
{
    public function __construct(
        $message = 'The requested site was not found on this server',
        $code = 404,
        $previous = null
    )
    {
        parent::__construct($message, $code, $previous);
    }
}