I'm kicked out of my AdminPanel, no authorization.
When your admin session expires the PHP session is dropped, where Ninja Security has stored a unique indicator of your authorization, before you logged in. Please note that not Ninja Security kicked you out of the admin panel, but Joomla did due to your expired session.
Regularly you would now be redirected to the login page, but due to the non-existent unique indicator NinjaSecurity denies access.
You will now have to use your Login Key in order to login again.