@Reacon Thank you! That did the trick. Worked perfectly on the first try.

Using add-on cars that get installed into the mods/update/x64/dlcpacks. I can only seem to do one at a time in the game. If I try installing more (that install the same way) it doesn't work. If I want to use a different add-on car, I have to remove one before it can work. Is that normal? And is there a way to work around this problem?