codeigniter MY_Controller not found

You would need to include your MY_Controller class or auto-load it. I suggest you auto-load it by adding the following to your application/config/config.php file.

function __autoload($class)
{
    if (strpos($class, 'CI_') !== 0)
    {
        if (file_exists($file = APPPATH . 'core/' . $class . EXT))
        {
            include $file;
        }
    }
} 

Make sure the filename is perfectly cased. Linux server is case-sensitive. So if the class name is My_Controller then the name of the file should be My_Controller.php

$config['subclass_prefix'] = "MY_"

check that in config.php and of course you should use it in Controller Name Like MY_Controller.php and Named "class MY_Controller...."