Please confirm that other people are not using your account. If you have shared your account information with other people, then you may be prevented from logging in to your account. If you are worried that others are accessing your account, you should change your password under your account profile.
The best way to prevent this error is to log out of your MLB Account every time you are finished watching games by clicking the log out button on the top right of any MLB.com page. The next time that you would like to watch a game, you will be prompted to login before the game launches.
If you have already seen this error message and you are sure that no one else is using your account, log out of your MLB Account, close all of your open browser windows and exit your browser. Next, re-launch your browser and click on the game that you would like to watch in the Multimedia Center. You will be prompted to log in again.