Why would security or authentication change when no manual changes were made in Server 2000? All of a sudden the server started requesting user names and passwords for connections that previously didn't require these. An example: there is a mapped drive, used to be able to click and the directory appeared, now prompts for username and password. Users are already logged into this domain and server because they are using Outlook connected to MS Exchange. A change that was made a couple of weeks before this happened a second server was added to the domain, it was set up as a second domain controller.
note: On the new prompts some time the user name has to be in the form of - firstname.lastname@example.org and sometime just the username, depends on workstation.