Message at logon doesn’t appear

Users are supposed to see a legal notice just before they log onto our network. Although we have set the Group Policy (both the “Message text for users attempting to log on” and “Message title for users attempting to log on” are defined) no message appears for users at logon. Two other sites are set up the same way and have no problems displaying the message. It’s just the third site that refuses to cooperate. We are running 2000 Server with W2k pro and XP clients. Any ideas would be greatly appreciated.