unable to recover ftp files

I have been trying for several days to retrieve the list of folders on my ftp servers, despite the various posts consulted I still cannot resolve an error.

I get this error: Warning: ftp_nlist() expects parameter 1 to be resource, bool given in D:WebwwwDesignindex.php on line 10

My code:

<?php
$serveur = '***';
$login = '***';
$pass = '***';

$ftp = ftp_connect($serveur, 21) or die('error connect');
$ftp_login = ftp_login($ftp,$login, $pass) or die('error login');

ftp_nlist($ftp_login, '.');
?>

Has anyone already encountered this problem?

The connection to the server is done well, $ftp & $ftp_login returns true

Thanks!