(Trackmania canyon)

Okay, when I download a car off the steam workshop, by hitting the subscribe button, I re-launch the game and the vehicle I downloaded appears. When I click on it to change the paint, then spend about 2 hours of work getting the paint on the car to look good. Once I hit the SAVE button, the game pauses for a second, then the screen goes black, a second later it says something about my driver crashing and the car is completely black. I would like some help as I really want to change my car's paint.