Account password problem

NT4 Domain with a 45 day password life-span.

Some users are prompted to change their password but when confirming their new password they get the error message that they don’t have permission to change it. On checking their account in user manager the only option checked is “user must change password at next login” NOT “user cannot change password”.

Any ideas what the problem is? Is it that they are trying to change password after 45 day period?