Me sale un error Fatal error: Call to undefined function define() in ...

[rdchava]

Me sale este error en mi página

Fatal error: Call to undefined function define() in /home/mi_usuario/public_html/index.php on line 15

Este es un fragmento hasta la línea 15 de index.php


<?php
/**
* @version $Id: index.php 14401 2010-01-26 14:10:00Z louis $
* @package Joomla
* @copyright Copyright (C) 2005 - 2010 Open Source Matters. All rights reserved.
* @license GNU/GPL, see LICENSE.php
* Joomla! is free software. This version may have been modified pursuant
* to the GNU General Public License, and as distributed it includes or
* is derivative of works licensed under the GNU General Public License or
* other free or open source software licenses.
* See COPYRIGHT.php for copyright notices and details.
*/

// Set flag that this is a parent file
define( '_JEXEC', 1 );


No tengo experiencia en PHP, pero según el error esta función no está definida.

Dónde la busco o qué hago?