Thank you for your answers but still no help:
I've changed these setting for a domain, verified that /var/www/vhosts/system/DOMAIN/etc/php.ini has changed accordingly, restarted apache, but I still have 500 Internal Server Error
I also tried this:
cd /var/www/vhosts/DOMAIN/httpdocs
su -c...
I've upgraded one of my servers to Plesk panel 11.5.30 so that I can use two PHP versions on the same server
Now both of PHP versiond don't work in CGI or FastCGI mode (500 internal server error)
Error log says:
(104)Connection reset by peer: mod_fcgid: error reading data from FastCGI...