I'm getting a confusing error when trying to setup Windows Authentication access to a new space. I already have it working in other spaces that I setup months ago. See first screenshot:
The most likely problem is with the service account used to access AD.
Check which one is used in the server settings and set the correct username/password. You may have a security policy that passwords must be changed periodically and the old password no longer works. Or the service account is locked/deleted for some reason.