I used the 3.5.1.8 version doing what you said and it still did not work, exiting still causes the "invalid pointer operation" error. I tried the 3.5.5.0 version and this time, I exited the file explorer app and refreshed my desktop before opening the app. I edited the 0-60 time of a particular vehicle to test it and it worked! But when I modified the hp and torque values and exit the application, that's when the same error, "invalid pointer operation" occurred when exiting. When I opened the game, the car said it had the 0-60 I modified it to but had the same performance. The hp and torque vales were the same too. I tried this again doing the same method but sadly did not work again.
Edit:
restarted my pc and opened the editor and now this shows up whenever exiting after modifying a car's data.