Unfortunately, I did not resolve it!
The version 5 I installed in a different directory seems to have the same problems...
If you need to have a look at it through FTP, the same access information I provided for version 4 now apply for version 5.
I've seen that this line is also written in the new index.php, but it does not work, anyway!
@ini_set('session.save_path', dirname(__FILE__).'/data/');
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