Can't select custom cars in the beta UI

When I try to drive the car I created it won't allow me to select it or customise it.

 

You've only made a skin?
Check to make sure your driver name in the newly created car is not the same as an existing driver. THEY NEED TO BE UNIQUE. It should work no problems in the new UI.

 

It's not the same but I can select it in the old ui just not in the new beta ui