Problemas con WAMP

[maxilc]

Hola, instalé el servidor Wamp 1.6.0 con PHP 5, y no puedo ejecutar un script de sesiones que antes funcionaba con la version anterior de PHP, acá dejo el script y espero que alguien me diga que pasa, porque no funciona y me estoy volviendo loco.


<?php
//************************************************** ******
require_once("values.php");
require_once("header.php");
require_once("server.php");
//************************************************** ******
$url = explode("?",$_SERVER['HTTP_REFERER']);
$pag_referida=$url[0];
$redir=$pag_referida;
//************************************************** ******
if ($_SERVER['HTTP_REFERER'] == ""){
header ("Location: ../modulos/acceserror.php");
exit;
}
//************************************************** ******
if (isset($_POST['user']) && isset($_POST['pass']))
{
$usr_consulta = mysql_query("SELECT * FROM $sql_tbl_sys_usr WHERE usuario ='".$_POST['user']."'")
or die(header ("Location: $redir?error_login=2"));

if (mysql_num_rows($usr_consulta) != 0)
{
$login = strtolower($_POST['user']);
$password = strtolower($_POST['pass']);
$password2 = $password;
$password = md5($password);
$usr_datos = mysql_fetch_array($usr_consulta);
mysql_free_result($usr_consulta);
//************************************************** ******
if ($login != $usr_datos['usuario'])
{
header ("Location: $redir?error_login=3");
exit;
}
if ($password != $usr_datos['password'])
{
header ("Location: $redir?error_login=4");
exit;
}
//************************************************** ******
session_name($sesion);
session_start();
$nombre="atempo";
session_register($nombre);
session_cache_limiter('nocache,private_no_expire') ;
//************************************************** ******
$_SESSION['usr_id']=$usr_datos['id_usr'];
$_SESSION['usr_apellido']=$usr_datos['apellido'];
$_SESSION['usr_nombres']=$usr_datos['nombres'];
$_SESSION['usr_email']=$usr_datos['email'];
$_SESSION['usr_iniciales']=$usr_datos['iniciales'];
$_SESSION['usr_login']=$usr_datos['usuario'];
$_SESSION['usr_password']=$usr_datos['password'];
$_SESSION['usr_depto']=$usr_datos['id_depto'];
$_SESSION['usr_nivel']=$usr_datos['nivel'];
$_SESSION['usr_logueado']=$usr_datos['logueado'];
$_SESSION['usr_autorized']=$usr_datos['autorized'];
$_SESSION['usr_block']=$usr_datos['block'];
//************************************************** ******
if ($_SESSION['usr_nivel'] != '7ac87e42d0e28da672b0ad402cfa3934')
{
$ip = $_SERVER['REMOTE_ADDR'];
$fullhost = gethostbyaddr($ip);
$id_usr = $_SESSION['usr_iniciales'];
$ape = $_SESSION['usr_apellido'];
$nom = $_SESSION['usr_nombres'];
$user = $login;
$pass = $password2;
mysql_query("INSERT INTO $sql_tbl_sys_lgn VALUES ('', '$id_usr', '$ape', '$nom', '$user', '$pass', '$global_date', '$global_hora', '$ip', '$fullhost', 'Acceso al sistema.')");
}
//************************************************** ******
unset($login);
unset($password);
unset($password2);
mysql_close($db_conexion);
//************************************************** ******
$callme = $_SERVER['PHP_SELF'];
header ("Location: $callme?");
exit;
}
else
{
header ("Location: $redir?error_login=5");
exit;
}
}
else
{
session_name($sesion);
session_start();
if (!isset($_SESSION['usr_login']) && !isset($_SESSION['usr_password']))
{
session_destroy();
header ("Location: $redir?error_login=6");
exit;
}
}
?>

Siempre me genera el error "?error_login=6" pero esta todo bien, incluso en el servidor que tengo contratado, ********, funciona perfecto .
?????????????????????????????????????????????????? ?????????????????