Hi, Kulga !
Kulga Website URL if available, screenshots of the error
URL : forum.devcube.fr
Screenshot : http://image.noelshack.com/fichiers/2016/44/1477991774-nouvelle-image-4.png
Kulga Ensure debug is set to true in config.php
I switched "debug" to true, but the error still the same.
Kulga What webserver software are you using - does it match the requirements?
I use Apache with PHP 5.6.26-0+deb8u1and MySQL 5.5.52-0+deb8u1 - (Debian).
Kulga What php version and extensions do you have? (in command line - php -m; php -v)
Here : http://pastebin.com/mu5qmbVt
Kulga Are you using a VPS or Shared Hosting?
I use my own VPS.
Kulga Relevant server error logs
Nohting in my error log ?
Kulga From root of your Flarum install, run this command in the command line php flarum info
http://pastebin.com/UKfnitcN
Kulga What have you tried so far?
I checked "url" in my config.php.
http://pastebin.com/x10v5yRy