Recently, GameSalad transitioned to a subscription-required model with a time-limited free trial. As a result, there is no longer a completely free version of GameSalad, and without a valid subscription, you cannot use the tool.
For more details on the reasons behind this move, as well as how it will affect existing users moving forward, please see this forum thread: http://forums.gamesalad.com/discussion/87424/state-of-gamesalad-on-6-30-2015/p1