You have tried to reassign your active drivers to make sure there's no problem there? If there is one then often the name of a different driver is listed in car repair than in setup, too. To save your drivers as the active ones again makes sure they are properly linked to a car in the games database.
I fixed this but forgot to reply about this. You can avoid this in the future when you sell an active driver. If you sell a driver, make sure he is a reserve driver first! :)
