It’s a simply weird and misleading error message. I was working on a client project which was actually based on Codeigniter (CI) framework version 2.1.3. Somehow, I did a typo in DB setting located at config/database.php file. But, I got a very weird error message: Fatal error: Class ‘CI_Controller’ not found in /var/www/my/……./system/core/CodeIgniter.php on line 233 as below….
At a first glance, it seemed that there was a bug in CI Core class. But, it was actually a misleading message. It should have been a database connection error. And, after tracing out the error message properly with xdebug (You must have xdebug installed in your PC to get the above error tracing), i got that there was error coming from DB drive. So, quickly checked the DB setting and fixed the typo. But, In the mean time, I already passed two hours for fixing. Finally, at least I saved my ass from losing two hours more.