When I join an online server in the demo or in S3 races, this “car ID error” appears when the race starts — both in the demo and S3. Should I be worried?
It may be when you entered some S3 server, picked a mod and joined, then left and joined demo server. LFS remembers last car you had and automaticaly tries to load it from garage in the next server. Before joining track you should always go in garage and select some available car.