Hi Till !
Still no luck. The same 500 Error ....
Fortunatelly I use VMware and I was able to make fast reverse to snapshot.
What else I could try ?
As an ideea, I use EZGenerator WYSIWYG webpage editor and the "Website Administration" module is not workig correctly on my ISPConfig server ( never worked ). That module require PHP-CGI also. Maybe is still a PHP-CGI problem on my server.
If necesar I can post any required files but I am not an Linux expert.
Thank you for your work !