Redirigiendo al usuario con sesiones

[kfh1992]

Mira ahor el error que me da

( ! ) Warning: Unknown: Your script possibly relies on a session side-effect which existed until PHP 4.2.3. Please be advised that the session extension does not consider global variables as a source of data, unless register_globals is enabled. You can disable this functionality and this warning by setting session.bug_compat_42 or session.bug_compat_warn to off, respectively in Unknown on line 0

<?php
session_start();
$mail=$_POST["mail"];
$password=$_POST["password"];
if ($mail&&$password);
{
include("../config.php");
$query = mysql_query("SELECT * FROM users WHERE mail='$mail'");
$numrows = mysql_num_rows($query);
{
while ($row = mysql_fetch_assoc($query))
{
$dbusername = $row['mail'];
$dbpassword = $row['password'];
$dbalias = $row['alias'];
$dbname = $row['name'];
$dbsurname = $row['surname'];
$permisos = $row['permisos'];
//
}
if ($mail==$dbusername&&$password==$dbpassword)
{
echo "Contraseña correcta";
$_SESSION['permisos'] = $row['permisos'];
switch ($_SESSION['permisos']) {
case "10":
echo "Eres admin";
break;
case "2":
echo "eres mod";
break;
case "1":
echo "usuario normal";
break;
}
//
}
else
echo "Contraseña errónea";
}
}
?>