Installing the Windows client doesn't require a license. Licensing is checked when the user attempts to log in to the repository, and if that is the reason for not allowing the connection, information to that effect is included in the message shown to the user. If the server thinks that your credentials are incorrect, it won't move on to the step where it checks licensing since it hasn't established the identity of the user. It sounds like this user is able to log in from another machine - are they following the same steps on both machines? Since you're trying to use Windows authentication, it could also matter what account they are logged in as.

And just a reminder that Laserfiche 10.3 has been out of support since 2022 and is no longer receiving security updates.