Sometimes it could be very helpful to read the FAQ )
4.10 When I use different car shapes the game crashes.1. Load the crashing car shape into Car Editor.
2. Go to Go to "File --> Export CTF" and save the file as "custom.ctf".
3. Load a car shape that does not crash.
4. Go to "File --> Import CTF" and import the "custom.ctf" to the shape.
5. Go to File --> Save As and choose a name for the new car shape.
I guess, usually this happens when you run carshape for GP3-2000 in GP31.13 or vice versa.