If you see that a 500 Internal Server Error has occurred, then something has gone wrong on the server.
To find out the cause of the error, learn PHP error logs or web server logs written at the time of the error occurrence.
You can enable tracking of PHP errors using free Logs app (install it via Installer) or by adding the following lines to file .htaccess:
php_flag display_errors Off php_value error_reporting 2147483647 php_flag log_errors On php_value error_log ./wa-log/php.log
With this setting changed, any messages of PHP errors will be saved to file wa-log/php.log. Use the records from that file to find out the cause of the server error.