Is it saying that when you try to report the sale of the vehicle? TurboTax can not calculate the sale of a vehicle (or other asset) that has varied in business percentage from year to year. So you can't report the sale in the vehicle section. You either need to manually calculate things and enter it in the "Sale of Business Property" section, or go to a tax professional.
if you used the standard mileage table for some years, then you need to look at the tables to find how much depreciation was included and include the standard mileage depreciation with the actual business depreciation taken in those years