Fatal error: Call to a member function on a non-object

Here is the ENTIRE error message I get:

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ERROR MESSAGE STARTS
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Fatal error: Call to a member function on a non-object in common.php on line 223

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ERROR MESSAGE ENDS
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Here is the file that the file it is referring to:

===============
FILE PHP CODE STARTS
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<?php
/***************************************************************************
 *                                common.php
 *                            -------------------
 *   begin                : Saturday, Feb 23, 2001
 *   copyright            : (C) 2001 The phpBB Group
 *   email                : support@phpbb.com
 *
 *   $Id: common.php,v 1.74.2.5 2002/12/17 23:59:37 psotfx Exp $
 *
 *
 ***************************************************************************/
/***************************************************************************
* phpbb2 forums port version 2.1 (c) 2003 - Nuke Cops (http://nukecops.com)
*
* Ported by Paul Laudanski (Zhen-Xjell) to phpbb2 standalone 2.0.4. Test
* and debugging completed by the Elite Nukers at Nuke Cops: ArtificialIntel,
* Chatserv, MikeM, sixonetonoffun, Zhen-Xjell. Thanks to some heavy debug
* work by AI in Nuke 6.5.
*
* You run this package at your sole risk. Nuke Cops and affiliates cannot
* be held liable if anything goes wrong. You are advised to test this
* package on a development system. Backup everything before implementing
* in a production environment. If something goes wrong, you can always
* backout and restore your backups.
*
* Installing and running this also means you agree to the terms of the AUP
* found at Nuke Cops.
*
* This is version 2.1 of the phpbb2 forum port for PHP-Nuke. Work is based
* on Tom Nitzschner's forum port version 2.0.6. Tom's 2.0.6 port was based
* on the phpbb2 standalone version 2.0.3. Our version 2.1 from Nuke Cops is
* now reflecting phpbb2 standalone 2.0.4 that fixes some major SQL
* injection exploits.
***************************************************************************/
/***************************************************************************
 *   This file is part of the phpBB2 port to Nuke 6.0 (c) copyright 2002
 *   by Tom Nitzschner (tom@toms-home.com)
 *   http://bbtonuke.sourceforge.net (or http://www.toms-home.com)
 *
 *   As always, make a backup before messing with anything. All code
 *   release by me is considered sample code only. It may be fully
 *   functual, but you use it at your own risk, if you break it,
 *   you get to fix it too. No waranty is given or implied.
 *
 *   Please post all questions/request about this port on http://bbtonuke.sourceforge.net first,
 *   then on my site. All original header code and copyright messages will be maintained
 *   to give credit where credit is due. If you modify this, the only requirement is
 *   that you also maintain all original copyright messages. All my work is released
 *   under the GNU GENERAL PUBLIC LICENSE. Please see the README for more information.
 *
 ***************************************************************************/

/***************************************************************************
 *
 *   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.
 *
 ***************************************************************************/

if ( !defined('IN_PHPBB') )
{
      die("Hacking attempt");
}

error_reporting  (E_ERROR | E_WARNING | E_PARSE); // This will NOT report uninitialized variables
set_magic_quotes_runtime(0); // Disable magic_quotes_runtime

//
// addslashes to vars if magic_quotes_gpc is off
// this is a security precaution to prevent someone
// trying to break out of a SQL statement.
//
if( !get_magic_quotes_gpc() )
{
      if( is_array($HTTP_GET_VARS) )
      {
            while( list($k, $v) = each($HTTP_GET_VARS) )
            {
                  if( is_array($HTTP_GET_VARS[$k]) )
                  {
                        while( list($k2, $v2) = each($HTTP_GET_VARS[$k]) )
                        {
                              $HTTP_GET_VARS[$k][$k2] = addslashes($v2);
                        }
                        @reset($HTTP_GET_VARS[$k]);
                  }
                  else
                  {
                        $HTTP_GET_VARS[$k] = addslashes($v);
                  }
            }
            @reset($HTTP_GET_VARS);
      }

      if( is_array($HTTP_POST_VARS) )
      {
            while( list($k, $v) = each($HTTP_POST_VARS) )
            {
                  if( is_array($HTTP_POST_VARS[$k]) )
                  {
                        while( list($k2, $v2) = each($HTTP_POST_VARS[$k]) )
                        {
                              $HTTP_POST_VARS[$k][$k2] = addslashes($v2);
                        }
                        @reset($HTTP_POST_VARS[$k]);
                  }
                  else
                  {
                        $HTTP_POST_VARS[$k] = addslashes($v);
                  }
            }
            @reset($HTTP_POST_VARS);
      }

      if( is_array($HTTP_COOKIE_VARS) )
      {
            while( list($k, $v) = each($HTTP_COOKIE_VARS) )
            {
                  if( is_array($HTTP_COOKIE_VARS[$k]) )
                  {
                        while( list($k2, $v2) = each($HTTP_COOKIE_VARS[$k]) )
                        {
                              $HTTP_COOKIE_VARS[$k][$k2] = addslashes($v2);
                        }
                        @reset($HTTP_COOKIE_VARS[$k]);
                  }
                  else
                  {
                        $HTTP_COOKIE_VARS[$k] = addslashes($v);
                  }
            }
            @reset($HTTP_COOKIE_VARS);
      }
}

//
// Define some basic configuration arrays this also prevents
// malicious rewriting of language and otherarray values via
// URI params
//
$board_config = array();
$userdata = array();
$theme = array();
$images = array();
$lang = array();
$gen_simple_header = FALSE;

include($phpbb_root_path . 'config.'.$phpEx);

if( !defined("PHPBB_INSTALLED") )
{
      header("Location: modules.php?name=Forums&file=install");
      exit;
}

global $forum_admin;
if ($forum_admin == 1) {
    //include("../../../db/db.php");
    include("../../../includes/constants.php");
    include("../../../includes/template.php");
    include("../../../includes/sessions.php");
    include("../../../includes/auth.php");
    include("../../../includes/functions.php");
} else {
    include("includes/constants.php");
    include("includes/template.php");
    include("includes/sessions.php");
    include("includes/auth.php");
    include("includes/functions.php");
}

//
// Mozilla navigation bar
// Default items that should be valid on all pages.
// Defined here and not in page_header.php so they can be redefined in the code
//
$nav_links['top'] = array (
      'url' => append_sid($phpbb_root_dir."index.".$phpEx),
      'title' => sprintf($lang['Forum_Index'], $board_config['sitename'])
);
$nav_links['search'] = array (
      'url' => append_sid($phpbb_root_dir."search.".$phpEx),
      'title' => $lang['Search']
);
$nav_links['help'] = array (
      'url' => append_sid($phpbb_root_dir."faq.".$phpEx),
      'title' => $lang['FAQ']
);
$nav_links['author'] = array (
      'url' => append_sid($phpbb_root_dir."memberlist.".$phpEx),
      'title' => $lang['Memberlist']
);

//
// Obtain and encode users IP
//
if( $_SERVER['HTTP_X_FORWARDED_FOR'] != '' )
{
      $client_ip = ( !empty($HTTP_SERVER_VARS['REMOTE_ADDR']) ) ? $HTTP_SERVER_VARS['REMOTE_ADDR'] : ( ( !empty($HTTP_ENV_VARS['REMOTE_ADDR']) ) ? $HTTP_ENV_VARS['REMOTE_ADDR'] : $REMOTE_ADDR );

      if ( preg_match("/^([0-9]+\.[0-9]+\.[0-9]+\.[0-9]+)/", $_SERVER['HTTP_X_FORWARDED_FOR'], $ip_list) )
      {
            $private_ip = array('/^0\./', '/^127\.0\.0\.1/', '/^192\.168\..*/', '/^172\.16\..*/', '/^10.\.*/', '/^224.\.*/', '/^240.\.*/');
            $client_ip = preg_replace($private_ip, $client_ip, $ip_list[1]);
      }
}
else
{
      $client_ip = ( !empty($HTTP_SERVER_VARS['REMOTE_ADDR']) ) ? $HTTP_SERVER_VARS['REMOTE_ADDR'] : ( ( !empty($HTTP_ENV_VARS['REMOTE_ADDR']) ) ? $HTTP_ENV_VARS['REMOTE_ADDR'] : $REMOTE_ADDR );
}
$user_ip = encode_ip($client_ip);

//
// Setup forum wide options, if this fails
// then we output a CRITICAL_ERROR since
// basic forum information is not available
//
$sql = "SELECT *
      FROM " . CONFIG_TABLE;
if( !($result = $db->sql_query($sql)) )
{
      message_die(CRITICAL_ERROR, "Could not query config information", "", __LINE__, __FILE__, $sql);
}

while ( $row = $db->sql_fetchrow($result) )
{
      $board_config[$row['config_name']] = $row['config_value'];
}

if (file_exists('install') || file_exists('contrib'))
{
      message_die(GENERAL_MESSAGE, 'Please ensure both the install/ and contrib/ directories are deleted');
}

//
// Show 'Board is disabled' message if needed.
//
if( $board_config['board_disable'] && !defined("IN_ADMIN") && !defined("IN_LOGIN") )
{
      message_die(GENERAL_MESSAGE, 'Board_disable', 'Information');
}

?>

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FILE PHP CODE ENDS
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My question is:

01. What is this error referring to specifically?
02. How can I fix the problem?

The website that uses this php script is:

http://www.saeyouth.net/network/modules.php?name=Forums

This website was severely hacked a very long time ago, and I have spent the day fixing the for reproduction. I honestly don't understand how to fix this problem.

-Panos