Erreur inconnue avec move_uploaded_file()

if (isset($_FILES['avatar'])) {
	$ds = $_SERVER['DOCUMENT_ROOT'] .'/images/avatars/';
	$ext = array('.png', '.gif', '.jpg', '.jpeg');
	$exd = strrchr($_FILES['avatar']['name'], '.');
	$fc = basename($_FILES['avatar']['name']);
	if (!in_array($exd, $ext)) {
		header('Location: account.php?al=bf');
	} else {
		$ms = 40000;
		$sz = filesize($_FILES['avatar']['tmp_name']);
		if ($sz > $ms) {
			header('Location: account.php?al=tl');
		} else {
			$fc = strtr($fc, 
          			'ÀÁÂÃÄÅÇÈÉÊËÌÍÎÏÒÓÔÕÖÙÚÛÜÝàáâãäåçèéêëìíîïðòóôõöùúûüýÿ', 
         			'AAAAAACEEEEIIIIOOOOOUUUUYaaaaaaceeeeiiiioooooouuuuyy');
    			$fc = preg_replace('/([^.a-z0-9]+)/i', '-', $fc);
    			if(move_uploaded_file($_FILES['avatar']['tmp_name'], $ds . $fc))
     			{
     				$upd = $bdd->prepare('UPDATE membres SET avatar = ? WHERE id = ?');
     				$upd->execute(array('/images/avatars/'.$fc, $_SESSION['id']));
          			header('Location: account.php?al=dc');
     			} else {
     				header('Location: account.php?al=errav');
     			}
		}
	}
}