Windows XP and network password change

Hi;
Something quite strange it’s happening in my network. We bought a month ago new machines with XP Pro installed. In all those machines, when their network passwords expire, it doesn’t ask you to change it, it doesn’t even warn you a few days before. Then users can log in with their old passwords but when they try to access outlook, it ask for the new password. I’ve check in group policy and make sure that the key “Interactive logon: Prompt user to change password before expiration” is set to 14 days. Help please.