You may be receiving an error due to a saved cookie on your browser from a previous login. Please click on this link which should remove any saved cookies from Classmates® while taking you to the login page, where you can enter your email address and a new password.
Please note also that if you previously saved your login information for Classmates in your browser such as Chrome or Firefox, you would need to go into that browser and either remove it completely or update it with your most recent password.