Aha sounds like he needs to disable it next time he manages to log in!Two Stage authentication which is otherwise known as Dual Factor Authentication is where you try to login with your credentials and then the site sends you a code that needs to be entered as well. This code can normally be sent to you using an email or via SMS, some systems allow you to use a code generator application that runs on your phone (such as Microsoft Authenticator, Authy and similar). If you dont enter the correct code in you do not login.
I am not familiar how this forum is using DFA as I have not enabled it on my account. You can enable it by going to your Password and Security settings.