We're running v 2.0.10 and have started getting reports that users are seeing the wrong user at the top of the forum screen. It only appears to happen to users that are currently logged in. Anyone have an idea of what is set wrong? When the wrong profile is shown the accompany unread post icons for the displayed profile also appear (it's as if one user is seeing anothers screen).
do you have any server level caching enabled? if so try to disable it.
This should help you and yes, it is most likely a server configuration issue:
http://www.simplemachines.org/community/index.php?topic=519868.0