When an ActiveDirectory user account has been disabled, it might render the user's mailbox in Exchange inoperative. Outlook will issue a vague object about being unable to access the folders. The event log on the Exchange server will record report a "log on" failure for the mailbox with the error code -2147221231. There is a fix. In ActiveDirectory, edit the user's properties under Exchange Advanced\Mailbox Rights. Make sure that at least one user has the 'Associated External Account' permission. If no user has that permission, assign it to the SELF account.
This issue is discussed by the Microsoft knowledge base entry KB278966.
