What's the car navigation's DVD copy protection?

The navigation DVD of my car (Blaupunkt Europa 2005) is getting scratched and I want to back it up.

In the past I thought there was no protection and so I tried to back it up with Toast Titanium 9.

Burning it in a dual- or single-layer DVD+R gets no practical result: the car says “BAD DVD”.

It makes me think there’s some sort of protection, but what? A guy @ VW has told me that the car checks if it’s a dual layer disk, but I don’t have such an amount of money (6 €/DVD) to waste while trying to backup the BE-2005.

Do you know about any kind of protection this DVD might have? Is ATIP reading possible?