[Plugin: TDO Mini Forms] error 500 with a custom plugin

Hi I made this to use a program with wordpress.

<?php
/*
Plugin Name: <font color="green">GWBBCODE Filter</font>
Description: Parse gwbbcode in your content for WordPress
Version: 1.0
Author: T_Clauss
*/
/*  Copyright 2008  T_Clauss  (email : T_Clauss@hotmail.com)

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/
function Wp_gwbbcodeinintialize(){
    echo "<b>GWBBCODE Filter</b>gwbbcode was written by: <b>Liu Pi</b>For more information on gwbbcode visit: <b>http://gwshack.us/</b>More Options comming Soon...";
}

function addmyplugintoasubmenu() {
    add_submenu_page('options-general.php', 'GWBBCODE Filter Options', 'GWBBCODE Filter', 10, __FILE__, 'Wp_gwbbcodeinintialize');
}
add_action('admin_menu', 'addmyplugintoasubmenu');

function Wp_gwbbcode($text) {
   $text = parse_gwbbcode($text);
      return $text;
   }
add_filter('the_content', 'Wp_gwbbcode');
?>

Now from the mysubmissions page when I click preiew i get an error 500.

also to get gwbbcode to work i need to include this.

if (!defined('GWBBCODE_ROOT')) {
define('GWBBCODE_ROOT', './gwbbcode');
require_once(GWBBCODE_ROOT.'/gwbbcode.inc.php');
}

Which I have inside <php? ?> in my index.php in wordpress, any suggestions? Posting from a form works fine just when doing the preview i get an error 500. I wasnt getting this b4 as it was working, all I did was change hosts. Same host different domain.