Try to do something really simple: Start a new empty scene. In the assemble room select the spline tool and click somewhere in the scene. The spline room should open. Click on the button with the square on it and drag a square on the vertical "drawing plane". You should get a rectangular object. Now go back to the assemble room. You should see the rectangular object where you originally clicked. If it doesn't work, post a screen shot of your assemble room and your spline room.