Login Form

Hi All, I have had a look around there and realise ye may be sick of haering this question but I really can't find the answer. I have a login script that will leave me log in but if I try to logout it says Fatal error: Call to a member function on a non-object in C:\xampplite\htdocs\project\db\check_login.php on line 21 logout.php <?php require 'db_connect.php'; if ($logged_in == 0) { die('You are not logged in so you cannot log out'); } unset($_SESSION['username']); unset($_SESSION['password']); //kill the session variables $_SESSION = array(); //reset the session array. session_destroy(); //destroy the session header('Location:index.php'); //redirect to index page ?> and check_user.php login 21 is $pass = $db->query("SELECT password FROM users WHERE username = '".$_SESSION['username']."'"); Any help would be greatly appreciated Regards, Ronan