I had to leave my car for a couple of weeks, and when I got back the battery was drained. After charging it, all seems to work normally, except that there's a warning on the display that a rear lamp is not working. None of the four parking/position lights (both front and rear) are working.

I've checked the lamps, relay 3, and fuses 19 and 21 in the rear fuse box. The number plate lamps, brake lights and headlights all work. I even unplugged the battery for a few minutes, and there's no difference.

I suspect that there are some other fuses and relays connected to this, but the manual only state these ones. I also think that the error is close to the lamps, as the computer knows that the lamps aren't working.

 

I managed to solve this. Turns out that the lights won't turn on if the battery isn't fully charged. It's a bit weird that you can start the car, drive it around with everything working fine, except for the parking lights.