Your namespace should be:

namespace Subfolder

And in routes:

Route::controller('/Main', 'Subfolder\MainController');

Ok that looks fine, but Laravel always show me this error:

Symfony \ Component \ HttpKernel \ Exception \ NotFoundHttpException

Controller method not found.

My controller now looks like this:

<?php
namespace Subfolder;

class MainController extends \BaseController {

	public function index()
	{
		dd('Main works');
	}

	public function getIndex()
	{
		dd('Main works');
	}

But still an error message.

Wow!!! That is nice.

I found in the log file that Laravel tries to call the "HomeController" instead of the "MainController". So I changed the order in the routes from this:

Route::controller('/', 'HomeController');
Route::controller('/Subfolder', 'Subfolder\MainController');

...to this new order:

Route::controller('/Subfolder', 'Subfolder\MainController');
Route::controller('/', 'HomeController');

And now the MainController is working.

Why is that so???

I think you need to remove the "/" from "/subfolder" so

Route::controller('Subfolder', 'Subfolder\MainController');