I try to create a private version and therefore I used something like this in php:

var scribd_doc = scribd.Document.getDoc( 28394353,  'xxx'); 
scribd_doc.addParam("use_ssl", true);
scribd_doc.addParam('public', false); 
scribd_doc.grantAccess("cbccf6e7-1ff7-9034-8a7c-a0c2a5b225ed", <?php echo "'" . trim($_COOKIE['PHPSESSID']) . "'" ?>, <?php echo "'" . scribd_calculate_signature($documentID = '28394353', 
    $sessionID  = trim($_COOKIE['PHPSESSID']),
    $userID     = "cbccf6e7-1ff7-9034-8a7c-a0c2a5b225ed") . "'" ?>); 
...
...

scribd_doc.write( 'embedded_flash' );

Which is the api of scribd for javascript with the addition of the signature. My result is the "Security failure - This is not a secure document but has security embed parameters" Error, which is not well documented. The document is set to private.

Any ideas?