It means that the file you have downloaded didn't have that kuid in it and it's not on your computer. I have ran into this a lot. Lot of times you can find one on your computer that will work as a replacement.
Open up the file in content creator plus
right click your car, go down to edit, then edit in content creator plus
Once it is open down at the bottom it should display the warnings and errors. Click on the one that says "kuid:65931:52003 is not recognized." It should take you to where it is. If not expand the tab on the left and go through the folders till you find it. When you find it if you don't know what it is suppose to represent, tell me what have that kuid value and I can help you find I replacement.