incomplete object

Får følgende fejl på min side:


Fatal error: main() [function.main]: The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "user" of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition in /usr/home/web/sth58909/mo/index.php on line 11

Mit script ser således ud

<?php
session_start();
require_once("db.php");
include("modules/user/class.user.php");
$db = new database;

if (!isset($user)){
    echo "Opretter ny class";
$user = new user($db);
}
echo $user->draw_user_menu();

?>

Det rigtige script er langt længere, men dette eksempel får samme fejl.
Har søgt google tyndt, men synes ikke rigtig at kunne finde et svar.