Recently I was working on a script on a fresh virtual server. The script was pulled from a production server and was being actively used. When I try to run it on the test server, it was mysteriously not working, Apache access_log shows 500 HTTP response code, PHP log_errors is ON,even display_errors is set to ON but there were no errors being displayed or logged. Thoroughly deducing my .htaccess, Apache virtual host configuration and doing a sanity check on the application itself, the mysterious error was being caused by one PHP extension missing, in this case php-ldap.