In una pagina del mio sito viene generato questo errore:
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/xxxxxx/public_html/calendario/index.php:2) in /home/xxxxxx/public_html/calendario/index.php on line 3

mi potete gentilmente dire dove devo spostare
codice:
if (!isset($_SESSION)) {
  session_start();
}
?

le ho provate tutte ma il problema non si risolve

ecco il codice intero



codice:
<?php require_once('Connections/server.php'); ?>
<?php
require("calendario/config.php");
require("calendario/lang/lang." . LANGUAGE_CODE . ".php");
mysql_connect(DB_HOST, DB_USER, DB_PASS) or die(mysql_error());
mysql_select_db(DB_NAME) or die(mysql_error());
$sql = "SELECT id, y, m, d, title, text, priv, TIME_FORMAT(start_time, '%k:%i') AS stime, ";
$sql .= "TIME_FORMAT(end_time, '%k:%i') AS etime, " . DB_TABLE_PREFIX . "users.uid, fname, lname ";
$sql .= "FROM " . DB_TABLE_PREFIX . "mssgs ";
$sql .= "LEFT JOIN " . DB_TABLE_PREFIX . "users ";
$sql .= "ON (" . DB_TABLE_PREFIX . "mssgs.uid = " . DB_TABLE_PREFIX . "users.uid) ";
$sql .= "WHERE (y*10000+m*100+d) > ";
$sql .= "(YEAR(NOW())*10000+MONTH(NOW())*100+DAYOFMONTH(NOW())) ";
$sql .= "ORDER BY y, m, d, start_time LIMIT 3";
$result = mysql_query($sql) or die(mysql_error());
?>
<?php
// *** Validate request to login to this site.
if (!isset($_SESSION)) {
  session_start();
}

$loginFormAction = $_SERVER['PHP_SELF'];
if (isset($_GET['accesscheck'])) {
  $_SESSION['PrevUrl'] = $_GET['accesscheck'];
}

if (isset($_POST['username'])) {
  $loginUsername=$_POST['username'];
  $password=$_POST['password'];
  $MM_fldUserAuthorization = "";
  $MM_redirectLoginSuccess = "amministrazione/modifica-assicurazioni.php";
  $MM_redirectLoginFailed = "index.php";
  $MM_redirecttoReferrer = false;
  mysql_select_db($database_server, $server);
  
  $LoginRS__query=sprintf("SELECT username, password FROM cai_utenti WHERE username=%s AND password=%s",
    GetSQLValueString($loginUsername, "text"), GetSQLValueString($password, "text")); 
   
  $LoginRS = mysql_query($LoginRS__query, $server) or die(mysql_error());
  $loginFoundUser = mysql_num_rows($LoginRS);
  if ($loginFoundUser) {
     $loginStrGroup = "";
    
	if (PHP_VERSION >= 5.1) {session_regenerate_id(true);} else {session_regenerate_id();}
    //declare two session variables and assign them
    $_SESSION['MM_Username'] = $loginUsername;
    $_SESSION['MM_UserGroup'] = $loginStrGroup;	      

    if (isset($_SESSION['PrevUrl']) && false) {
      $MM_redirectLoginSuccess = $_SESSION['PrevUrl'];	
    }
    header("Location: " . $MM_redirectLoginSuccess );
  }
  else {
    header("Location: ". $MM_redirectLoginFailed );
  }
}
?>