Outlook 2000

I recently added a second exchange server 5.5
to our domain, I moved half the mailboxes
to the new exchange server. We ran into
licensing issues as I had installed an MDSN
version of Winnt 4.0 which I have been
told is hardcoded to a 10 user license.
I spent most of yesterday moving mailboxes
back to the first exchange server. Now
when someone changes their view to view by sender,it does not indicate any unread messages by the sender’s name. The inbox
shows 30 unread messages though.What can
I do to restore the ability to view by sender
and it working.