I can help you!
Maybe...
but, I had the same problem to. The one I know, you cn't group something, and group it again(double group).
If I fac the same problem, i explode it, and regroup it.
If it won't work, try if you double group something, ex: you group a car rim, and group the rim with the tyre, the rim will be invisible. Solution : open the group, and explode rim group. or explode the group, unselect(CTRL+SHIFT+click) rim group, and group the tyre.

You're amazing!
I wanna ask if you can record your way to make car and upload it on you tube?
I interesting your way making that vw on the first video.
I made some cars, bad. then, this is some the renders

@gaieus said:

Hi XamalA,

That person must have used groups/components which is the ideal way of separating geometry in a model. You can read further about them here:
http://download.sketchup.com/sketchuphelp/gsu6_win/Content/G-Entities/Ent-Group.htm
and here:
http://download.sketchup.com/sketchuphelp/gsu6_win/Content/G-Entities/Ent-Component.htm

BTW - I cannot see your attachment.

I'm sorry, I can't attach the file because it's more than 9mb.

I've made a lamborgini muricielago, and mitsubishi galant. I've made them all with intersect technique.
But, the final model can't be a complex and great model. I've looking on 3d warehouse, and someone made an awesome car. I take one example. I've download porsche 911 gt, explode it, and move the front bumper. And I saw something I can't believe. That car made like a real car with a bodykit. the cumper, sideskirt, is just the bodykit. It's look like a 'naked' car, and the bodykit placed outside. Cool,
Anybody can help me?
(I attach the car i've download)