Users are not able to change their password at password expiration prompt

I have Windows 200 Advance server, we have ipmplemented the password policy so that password should expire in every 45 days, but user’s prompted to change their password at the time of login they get the message that you don’d have permission to change your password. I have given every one password chang rights at the domain controller object.

I dont know why is it happening.
if some body can help me out.