I checked on your setup. You assigned the bounding face of the radiator to the car boundary condition (no-slip wall). As the radiator is defined as a porous medium (advanced concept) it's bounding faces can not be assigned with boundary conditions. See in the instruction:
Select all the entities starting with solid_0 except solid_0_Reartire and solid_0_Fronttire
So you simply need to remove the face RadiatorZone_boundingFaces from your boundary condition. What I mentioned above holds true for both MRF zones as well as porous media zones. The error message is misleading in your case as it did not hint on porous media. I created a ticket for this.