Knit to solid doesn't work every time, you can try the "thicken" command to turn a closed surface to a solid, the option will only appear within the thicken command when it is possible to do.
If It's not possible to do that would suggest your model has a hole, which it does.
Attached screenshot shows you have two holes in your surface model
Thank you very much. I find problem by your image and fix it. So now I have full solid body. But I still need to do shell from it. Because it will be very expensive if I print full solid car.
Problem is: When I get shell and check bottom of the car write me error massage:
" Thickness value is greater than the Minimum radius of Curvature. The shell may succeed, but could cause undesirable results, such as bad geometry. To find the Minimum radius of Curvature, use Tools, Check."
If i click OK, then show me some parts (maybe that parts are wrong), but I have no idea what is wrong with them and how to fix it.
Please help me If you know what is wrong and tell how to fix it, or send shelled that solid.
Thank you very very much.
(I add solid car)
bmw 10.SLDPRT.zip 4.0 MB