One user not able to see shared calendar
 

I have one exchange 5.5 server running on NT4 with Outlook XP/2000
clients. I have one user who has a shared calendar. On the outlook
client, the calendar is shared for several users as a reviewer. All
but one user can view the calendar. When we try to expand the mailbox
where teh shared calendar resides, we get an error.

I matched security settings from a user who CAN see the mailbox, with
the user who CANNOT. Nothing seems to help... Any suggestions?