Problemas con sesiones

[Calamaro]

este es parte del codigo
if ($action == "PreviewPostal") {
session_start();
$variables_formulario[0] = $nombre;
$variables_formulario[1] = $mail;
$variables_formulario[2] = $nombredest;
$variables_formulario[3] = $maildest;
$variables_formulario[4] = $mensaje;
$variables_formulario[5] = $maildest2;
$variables_formulario[6] = $maildest3;
$variables_formulario[7] = $maildest4;
$variables_formulario[8] = $maildest5;
$variables_formulario[9] = $id;