We are running Exchange server 2003 with service pack 2, which is supposed to
correct the issue listed in KB article 885924
(http://support.microsoft.com/kb/885924/en-us)

However, when attempting to open a mailbox from Outlook, we still receive
the same error message.  Permissions have been granted to the mailbox for
testing.  Can anyone shed some light on possible reasons why we receive a
"Unable to display folder" message?

Migrating from Exchange 5.5 to 2003
Identify the owner of a Drag/Drop item in a Public Folders
Migration Wizard Fails at Groupwise Domain
Exchange OWA Login and domain question.
Emails stuck in SMTP (mainly Hotmail and MSN addresses)