Problemas de cabeçalho do site

Olá, fiz o sistema de login e senha no dreamwever e enquanto estava no localhost funcionava tranquilo, mas quando coloquei no servidor deu este erro:

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/santo458/public_html/admin/header.php:3) in /home/santo458/public_html/admin/header.php on line 17
O código é esse:

<?php include"../Connections/config.php";

 $conexao = mysql_connect("$hostname_config", "$username_config", "$password_config")
 or die ("Erro ao conectar com o banco de dados. Por favor nos informe no e-mail contato@upinside.com.br!");
 $db = mysql_select_db("$database_config")
 or die ("Erro ao selecionar a base de dados. Por favor nos informe no e-mail paroquia@santoantoniobarbalha.com.br!");

 ?>

<?php

//initialize the session

if (!isset($_SESSION)) {
 session_start();
}
?>

<?php

// Logout the current user.

$logoutAction = $_SERVER['PHP_SELF']."?doLogout=true";
if ((isset($_SERVER['QUERY_STRING'])) && ($_SERVER['QUERY_STRING'] != "")){
 $logoutAction .="&". htmlentities($_SERVER['QUERY_STRING']);
}

if ((isset($_GET['doLogout'])) &&($_GET['doLogout']=="true")){
 //to fully log out a visitor we need to clear the session varialbles
 $_SESSION['MM_Username'] = NULL;
 $_SESSION['MM_UserGroup'] = NULL;
 $_SESSION['PrevUrl'] = NULL;
 unset($_SESSION['MM_Username']);
 unset($_SESSION['MM_UserGroup']);
 unset($_SESSION['PrevUrl']);

 $logoutGoTo = "../index.php";
 if ($logoutGoTo) {
 header("Location: $logoutGoTo");
 exit;
 }
}
?>
<?php
if (!isset($_SESSION)) {
 session_start();
}
$MM_authorizedUsers = "";
$MM_donotCheckaccess = "true";

// *** Restrict Access To Page: Grant or deny access to this page

function isAuthorized($strUsers, $strGroups, $UserName, $UserGroup) {
 // For security, start by assuming the visitor is NOT authorized.
 $isValid = False;

 // When a visitor has logged into this site, the Session variable MM_Username set equal to their username.
 // Therefore, we know that a user is NOT logged in if that Session variable is blank.
 if (!empty($UserName)) {
 // Besides being logged in, you may restrict access to only certain users based on an ID established when they login.
 // Parse the strings into arrays.
 $arrUsers = Explode(",", $strUsers);
 $arrGroups = Explode(",", $strGroups);
 if (in_array($UserName, $arrUsers)) {
 $isValid = true;
 }
 // Or, you may restrict access to only certain users based on their username.
 if (in_array($UserGroup, $arrGroups)) {
 $isValid = true;
 }
 if (($strUsers == "") && true) {
 $isValid = true;
 }
 }
 return $isValid;
}

$MM_restrictGoTo = "index.php";
if (!((isset($_SESSION['MM_Username'])) && (isAuthorized("",$MM_authorizedUsers, $_SESSION['MM_Username'], $_SESSION['MM_UserGroup'])))) {
 $MM_qsChar = "?";
 $MM_referrer = $_SERVER['PHP_SELF'];
 if (strpos($MM_restrictGoTo, "?")) $MM_qsChar = "&";
 if (isset($_SERVER['QUERY_STRING']) && strlen($_SERVER['QUERY_STRING']) > 0)
 $MM_referrer .= "?" . $_SERVER['QUERY_STRING'];
 $MM_restrictGoTo = $MM_restrictGoTo. $MM_qsChar . "accesscheck=" . urlencode($MM_referrer);
 header("Location: ". $MM_restrictGoTo);
 exit;
}
?>

Alguém pode me ajudar?