I tried to remove that block but without success, under the root directory of phplist I’ve this .htaccess that contains some restrictive rules:
http://www.francescoparisionline.it/htaccess.txt
I’m wondering if this <FilesMatch "(index.php|dl.php|ut.php|lt.php|download.php|connector.php)$"> is the part that causes the 403 error when I try to access to: securimage/securimage_show.php