How to fix Lightning index.php problem

If you get index.php problem message, that means Lightning was unable to modify your root index.php automatically.

Edit your index.php and after this code:

// Install
if (!defined('DIR_APPLICATION')) {
    header('Location: install/index.php');
    exit;
}

insert this line:

if (file_exists($li = DIR_APPLICATION.'/controller/extension/lightning/gamma.php')) require_once($li); //Lightning