I just installed a secondary domain controller on a 2003 platform and whenever I disconnect the first domain controller the secondary one is not allowing new users to logon. Also, when the new domain is up users are unable to send/receive emails/ or browse the Web.
This new domain is also a DHCP/DNS servers. It does issue IP addresses and whenever users logon to the domain and I can see them under the security/Event Logs.
Basically, when the new domain is up it is not allowing users to do their normal tasks.
Note: Active Directory works fine. Changes on the old or new is quickly replicated between the two domains.