In our efforts to increase security in CodeChef, we have restricted log-in into an account from only one system at a time. So, now if a user is already logged in from a system and she logs in again from a different system then she will be logged out from the previous one. The feature also holds for team login. So now one team can be logged in from only one system. If users face any issue, please send a mail to firstname.lastname@example.org.