I'm self employed and sold a business vehicle. How can I fix the following error: "For Disposition calculations, depreciation cannot exceed business basis."

Your basis is what you paid for the car (plus invested in it if you have any major improvements that you made).  The amount of depreciation can't be more than what you paid for the car.  Currently, on your return, it is.  You need to adjust it so the depreciation is less than or equal to the amount that you paid for the car.

TurboTax is not set up to report a sale of an asset that has varied in business percentage from year to year (such as a vehicle).

You would need to say it was converted to personal use in the vehicle section, then MANUALLY calculate things and enter that in the "Sale of Business Property" section.  Or go to a good tax professional this year.