You will see a Failed Tech error message if the set up file for the car does not pass inspection.
iRacing will provide setups for all official car and track combinations that are in an official iRacing series.
If you are using a car and track combination that is not in an official iRacing series, the setup may not be a good one.
You can either create your own setup (more information on that you can find HERE in the Setups and Tools section), in the FORUMS or some third party websites.