I can't get the Basic Motion feature to work when applying motors, contacts, gravity, etc.  Everything works just fine as an animation, but when I switch to the "Basic Motion" tab and click the "calculate" button, the time bar turns red and nothing happens.  I've tried to apply the different features (motors, gavity, contacts, etc.) to a number simple and complex models, but can't get basic motion to do anything.

Any ideas?  Thanks.