Recently I have a problem that new Active Directory users cannot log into Sharepoint.
All other functionality seems fine, but it appears to be failing to create new user accounts.
To me, it looks like the FIM service was never setup and working so it appeared to be validating users in a different way, but I am not sure how this used to be working.
The only change which has occured between new users being able to log in was a rebuild of the primary domain controller after it had a corrupted disk. This means that the primary domain controller has been changed to a new server, although I cannot see why this might cause an issue.