If you change something on the server, install a phpBB extension or change config files, it can happen that you can no longer access your forum and instead only get errors 500 internal server error received as a message.
However, that doesn’t help much, since you can’t see what the server doesn’t like. To change that, you can display the exact errors.
You do that as follows:
Open: the file
.htaccess in the root folder
Find the following text:
<IfModule mod_rewrite.c> RewriteEngine on
Then add the following on a new line:
php_flag display_errors on
The line causes PHP to now display the errors instead of just an all-white page or 500 error.
Now you can see more precisely what the server doesn’t like. Once you have fixed the problem, you can of course deactivate it again by simply commenting out the line you just added: #php_flag