Cannot add user to any public group

[tlstevens]

There are several public folders set up in our exchange 2000 environment. I can add permissions to these folders for all but one user. I cannot give him permission to any public folder. I add him to the group of users who have access to a folder, grant permissions, click ok. Once I go back in to the permissions screen that user is no longer in the list. I've done this from the client side as owner of the folder and from the system side. I'm not getting any errors, and not seeing any in the event log, although I may not have my logging set high enough. Any ideas would be warmly welcomed!