What happens when I click on a "Free Model", I get a redirect.
I have a screen grab of your website below. When I click on the "Kombi 1.4 Flex Bus", I get the next page, (I had to cross out my private information. This happens on every link I click on your website. I have Norton full security and I build computers, it is not a problem on my end. The fact that it ends up in Portuguese proves this.
Your Site:
Then the re-direct to Google. (probably where your problem is), I had to remove my address for privacy, I follow through, as this is an account I use for testing, and sign in:

Then I get the following Page after signing in to Google, there is a redirect on your free model downloads, asking you to sign in with Google, even signing in with Google, you then the
Permissao necessaria. Quer entrar? Peca acesso ao proprietario ou acesse com uma conta que tenha permisao.
(Kind of obnoxious, seeing how I did all the steps)
This is costing you a lot of website traffic loss! Again, I had to remove my private data, I'm just trying to help you find the problem.

:
