This error will occur when a user cancels the Google Play Games/Game Center login over 3 times inactivating it. You will need to activate your Google Play Games or Game Center again by logging in from Setting or Game Center app first, then enter the game.
Google Play Games (usually looks like a controller) is a app that should should be on your phone. If not you can download it from here:
Please make sure you are logged in there, if not log out and log back in again before trying to get into Mini Motor WRT again.