You cannot define a new game because your null level does not allow you to play more than 5 games at once and you are already playing (including your game invitations) 5 games.
You can solve this unpleasant situation by upgrading your membership.
(hide) If you want to always be warned about the latest post on a discussion board, you can receive the posts on your news client by clicking the RSS logo at the top right of each board. (pauloaguia) (show all tips)