Update query werkt niet

<?php
session_start();
	ini_set('display_errors',1); // 1 == on , 0 == off
	error_reporting(E_ALL | E_STRICT);
	if ($_SERVER['REQUEST_METHOD'] == 'POST') {
//Hier checks op de invoer
              if (count($_SESSION['error']) == 0) {
			try {
				require_once ('data/link.php');
				$sql = "UPDATE members SET auth=:auth, period=:period WHERE id = :id";
				$stmt = $db->prepare($sql);
				$stmt->execute(array(
								':id' => $_SESSION['id'],
								':auth' => $_POST['auth'],
								':period' => $_POST['period']
						));
				if($stmt->rowCount() == 0) {
					throw new PDOException('Er zijn geen rijen gewijzigd in de UPDATE query.');
				}
			}
			catch(PDOException $e) {
				echo 'Foutmelding: '.$e->getMessage().' op regel '.$e->getLine();
				header ('Refresh: 2; url=nieuwe-aanmelding.php');
				exit();	
			}
		}
        }
	try {
		require_once ('data/link.php');
		$sql = "SELECT id, firstname, lastname, username, email, randomcode FROM members WHERE randomcode=:randomcode";
		$stmt = $db->prepare($sql);
		$stmt->execute(array(
						':randomcode' => $_GET['key']
					));
		sleep(1);
		//Get the results from the database and close the connection
		$result = $stmt->fetchAll();
		if (count($result) == 1) {
			$_SESSION['id'] = $result[0]['id'];
			$_SESSION['firstname'] = $result[0]['firstname'];
			$_SESSION['lastname'] = $result[0]['lastname'];
			$_SESSION['username'] = $result[0]['username'];
			$_SESSION['email'] = $result[0]['email'];
			$_SESSION['randomcode'] = $result[0]['randomcode'];
		}
		else {
			echo 'Geen resultaat gevonden.';
			exit;
		}
	}
	catch(PDOException $e) {
		echo 'Foutmelding: '.$e->getMessage().' op regel '.$e->getLine(); 
	}
?>

<tr>
						<td><label for="firstname">Voornaam:</label></td>
						<td><input type="text" name="firstname" value="<?php echo isset($_SESSION['firstname']) ? htmlspecialchars($_SESSION['firstname']) : '' ?>"/></td>
					</tr>
					<tr>
						<td><label for="lastname">Achternaam:</label></td>
						<td><input type="text" name="lastname" value="<?php echo isset($_SESSION['lastname']) ? htmlspecialchars($_SESSION['lastname']) : '' ?>"/>
					</tr>
					<tr>
						<td><label for="email">Emailadres: </label></td>
						<td><input type="text" name="email" value="<?php echo isset($_SESSION['email']) ? htmlspecialchars($_SESSION['email']) : '' ?>"/></td>
					</tr>
					<tr><td><input type="text" name="check" id="check" /></td></tr>
					<tr>
						<td><label for="authorisatie">Authorisatie: </label></td>
						<td><input type="radio" name="auth" value="1" />Ja&nbsp;
						<input type="radio" name="auth" value="0" />Nee&nbsp;
					<tr>
					<tr>
						<td><label for="periode">Geldigheidsduur: </label></td>
						<td><input type="radio" name="period" value="1" />Oneindig&nbsp;
						<input type="radio" name="period" value="0" />Eén week;
					<tr>
						<td>&nbsp;</td>
						<td><input type="submit" value="Verstuur" id="button"/>
						<input type="reset" value="Wissen" id="button" /></td>
					</tr>