This is a recurring/intermittent problem. Exchange 2003. User on the LAN changes his/her password. Can access email, etc. Goes home and tries to access OWA on a MAC and gets the internal 500 error. After this occurrence, it is not possible to log in to this users email using OWA from ANY computer, PC or MAC. IF the user's account is modified in some way, removed/added back to a group membership, access to email using OWA is restored.