It's actually because you just installed something the wrong way. Mostly happens when it's a car that is included in both spawns, you can check it out by driving with the Admiral you've been given and, seeking for the car you replaced, if you can use it, then that's the problem, if you get in and closes, that's the problem too. (This is what happens to me)
Re-install the game and, let the default bike (Or the car you want to be replaced) go over.
Or ask a skilled member to create a specific car/bike skin/model.--------------
If you're using Spoosh (Assuming you said "Spawn a car" and not "spawning the cars") then the problem is the exe. My case was that, it just closed and, it popped a window with an Unhandled Exception.
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Go try the old school method as well, try all the fucking compatibility modes
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