You configured your Alfresco with passthru which is no longer supported and not a good option anyway. You should switch to kerberos. I bet a windows server update killed your passthru authentication with the latest windows update. By enableing ldap authentication you will be able to authenticate users as defined in your ldap config which is:
but only the ones sitting directly in users,dc\=domain_name,dc\=intern
You are right, the problem appeared after a windows update.
I've taken out the passthru settings and CIFS ones in the config file and restarted alfresco, but the same problem - admin account can login, the rest of the users not (i get the same error message Your authentication details have not been recognized or Alfresco may not be available at this time.).
Do I need to setup kerberos for the login to work properly for the other users? I thought to leave this out for now.
Here is the updated settings file (red line is added as Caesar's post recommends)