This question has been answered by breezer. See the first response.
when you go to FTP and rename index.php does your site still works?Good idea, tested and my side stops working as soon index.php is renamed.
maybe your host moved the site and your FTP uses some IP instead of ftp.domainname.com
you sure you did an install?Yes, twice. After each time I set the hook to remove the install folder and it was removed as expected.
Have a look at manager/includes/version.inc.phpMany thanks for the hint. File was NOT overwritten. So I uploaded/overwrite all files by FTP instead using the Plesk-tool and all went very well.