I upgraded a single 2k DC to 2k3 (have good images but am willing to avoid going back). After adprep/forestprep, adprep/domainprep and setup computer boots well, admin able to login, but existing Exchange mailboxes (not yet upgraded to 2003) inaccessible to users (admin can access). I remarked that network shares also became inaccessible. Ever seen? any clue?

Sounds like some security settings/firewall got updated in the upgrade. Might take a look at this: http://support.microsoft.com/default.aspx?scid=kb;en-us;555040

Thank you. I am checking it. I did not mention, but after first bumping into the problem I thought that it was due to the fact that the Exchange server was not updated to 2003. Therefore (stupid me) I decided to upgrade Exchange. Sure, the problem is still here. This almost brings me to the conclusion that what went wrong was the AD migration. I think that I will reapply adprep before doing anything else. What do you think? Thanks in advance. Abel