With a fresh clone or ZIP download, clicking on the Torque Toolbox's Play Game button will crash the Toolbox. The work around is to first create a new project based on one of the templates.
The solution is to correct this when the open source version of the Toolbox is released.
First reported: http://www.garagegames.com/community/blogs/view/21886/3#comment-187339
Discussed cause: http://www.garagegames.com/community/blogs/view/21886/3#comment-187351
New version of the Toolbox has been checked in to fix this issues. The Toolbox has also been renamed from Torque 3D.exe to Torque 3D Toolbox.exe.