Outlook 2000 Error Opening Task Request

I have a user who cannot open his tasks in his Microsoft Outlook 2000 inbox. He receives the error message "Can't open this item." Could not complete the operation. One or more parameter values are not valid." This same task is sent to 18 different people and he is the only user who cannot open or delete these tasks. Microsoft's Q241243, says this error occurs when a person receives an assigned task that used a user-defined keywords field on a task form. They are not using a user-defined keywords field on a task form. They just use the original task object in Microsoft without modifications. The problem also follows this user from workstation to workstation. Wehave tried moving this user's mailbox to another server. We have archived and exmerged his mailbox, re-created it and merged the data back, but nothing seems to help. Can Someone please help.