I'm trying to use Newton for my car physics, but I'm having two big problems.

When I run the level I get a "crash in NewtonVehicleAddTyre" error before the level starts for each of the four tires.

Then when the level starts the tires stay in place and the body of the car falls through the floor. I'm using a model for the track the car drives on and I don't know if that has anything to do with it. Also, I've seen a lot of posts about the .cls file, but I don't know how to create it or where to find it.

Can anyone help?