As Seahawk says, you must put in the game folder also the file that he has linked, and use only
that one, which is the most updated one, and not use those included in the cop cars release archives, because they're not updated like
that one.
If you get a game crashing problem, it could be because you're having too much add-on cars in your game folder. Remove some of them, especially those with the bigger .ar file size.