Ok, I managed to get the V24 software and I tried to install it in the nav unit.
Sadly enough, I still have the same symptoms as before.
If i turn the ignition key on and then put the cd in the unit, it doesn't seem to be able to read it.
If i turn the ignition off (with the cd still in it), I can hear that it is reading for maybe 8-10 seconds after bootup. I then also get the message as decribed before "Software - CD im navigationsrechner. Software wird geladen".
After this, nothing happens. The only sound from the nav unit is the cooling fan in the back.
I'm starting to suspect a faulty laser. Does this sound totally off target??