"There is no such object on server" when retrieving MailBoxRights   

Using the MailboxRights property of IExchangeMailBox interface, I get an 
exception saying "There is no such object on the server". I know that the 
mailbox exists and that it's beeing used. What could cause this?

date: Thu, 23 Jun 2005 07:39:18 -0700   author:   Bjørn Terje Svennes