Erro php - Session

Pessoal, troquei de hospedagem e agora está dando erro na minha página global.php

o erro é o seguinte:

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/brteam/public_html/me.php:1) in /home/brteam/public_html/global.php on line 24

segue abaixo o código da pagina global.php :

<?php
ob_start();

//Installation files? - Start if(file_exists('ainstall.php')) {

echo 'Go to <a href="install.php">install.php</a>';
die;
}

if(file_exists('aupdate.php')) {

echo 'Go to <a href="update.php">update.php</a>';
die;
}

//Installation files? - End

define('SEP', DIRECTORY_SEPARATOR);
$dir = str_replace('register'.SEP, '', dirname(__FILE__).SEP);
$dir = str_replace('functions'.SEP, '', $dir);
$dir = str_replace('housekeeping'.SEP, '', $dir);
define('DIR', $dir);
define('DOCUMENT_ROOT', DIR.SEP);
define('INCLUDES', DIR.'inc'.SEP);
define('WWW', 'http://'.$_SERVER['SERVER_NAME']);

session_start();

require_once DOCUMENT_ROOT.'config.php';

$connect = mysql_connect($host, $username, $password) or die("Could not connect to server, error: ".mysql_error());
mysql_select_db($dbname, $connect) or die("Could not connect to database, error: ".mysql_error());

require_once INCLUDES."class.core.php";
require_once INCLUDES."class.users.php";

$core = new Core();
$users = new Users();

require_once DOCUMENT_ROOT.'lang/'.$language.'.php';

define('MAINTENANCE', $core->Maintenance());

if(USERNAME_REQUIRED == TRUE && !isset($_SESSION["username"]))
header("Location: ".WWW."/characters.php");
if(ACCOUNT_REQUIRED == TRUE && !isset($_SESSION["account"]))
header("Location: ".WWW."/index.php");

$sitename = $core->CmsSetting('cms_name');

if(isset($_SESSION["username"]))

{ $username = $core->EscapeString($_SESSION['username']); if($users->CheckBan($username))

header($users->BanInfo($username));
}

if(MAINTENANCE && !$users->UserPermission('hk_login', $username) && !defined('MAINTENANCE_PAGE'))

header("Location: ".WWW."/maintenance.php");
?>

alguem saberia corrigir esse problema?

Agradeço desde já.