This message indicates that you have tried to exceed your user limit for licenses on MDCC. Grace period is set to 60 days and starts the first time you exceed your license limit. The IBM licensing allows you to go over the limit for 60 days from the first time you exceed your user limit. Once you reach 60 days after exceeding your limit, IBM licensing programs will no longer allow you to exceed your limit. Once you reach your license limit of users the very next user that attempts to sign in will not be allowed and the Grace Period Expired Message will be generated.
There is nothing that can be done to avoid this message other than increase the number of licensed users.