set 404 custom error

Hi, if i set 404 error with this route (where Errors is the name the controller and show404 the method), i have a php error: Class 'Errors' not found.

Code:

$routes->set404Override(Errors::show404);

if i set error with this route the page 404 work.

Code:

$routes->set404Override(function(){echo view('show404.php');});

Why? Where i wrong?

Thanks for the support.