Configs usually aren't JSON, but I'm not familiar with Personal Cars so I'm not sure. The file type would be .json if your system displays file types after file names. Here's a JSON validator: jsonlint.com
For good measure, revert the config changes you made or delete the config so it's regenerated. Maybe that false or is causing the error, or something else was accidentally changed.
After seeing the full list of mods though, if the issue isn't a config problem, you should test for incompatibilities. Try running MC with just Personal Cars to see if you still get the error. If not, this is an incompatibility and there is a common strategy for identifying it. The folder naming scheme is up to you:
- Move half of the mods from the mods folder into a new folder named 1
- Run MC to check again for the error.
- If the error persists, return to step 1 but name the new folder 2, and so on until the error stops.
- Move any remaining mods from the mods folder (except Personal Cars) into a new folder named Good.
- Move the mods from the highest number folder back into the mods folder with Personal Cars.
- Return to step 1 until only Personal Cars and the culprit(s) are in the mods folder.
- Move any remaining mods (except Personal Cars) into a new folder named Bad.
- Move all the mods from Good and the numbered folders back into the mods folder with Personal Cars.
There's a low chance that multiple mods in combination with Personal Cars cause the error, in which case you may need to repeat the whole process again. Though not very straightforward, this strategy is faster than removing one mod at a time. When the process is complete, report the incompatibility to Personal Cars and any mod in the Bad folder.