404 in CodeIgniter3 application

I am trying to solve a problem of 404 in my COdeIgniter3 application. 
The problem occurs because of problem in core/Codeigniter.php:
echo 'BEFORE call_user_func_array';
var_dump($CI, $method, $params);
call_user_func_array(array(&$CI, $method), $params);

// Mark a benchmark end point
$BM->mark('controller_execution_time_( '.$class.' / '.$method.' )_end');
echo 'AFTER call_user_func_array ';

BEFORE is displayed, AFTER is not displayed.
var_dump displays object Main, method index, empty array params.
I have a controller
class Main extends MY_Controller {
public function index() {
...

In folder /home/robert/Projekty/praca/application/controllers I have 
file Main.php
In file /home/robert/Projekty/praca/application/config/routes.php I have:

$route['default_controller'] = 'main';
$route['404_override'] = '';