After some research, I read on Wikipedia that SD cards over 1 GiB are adressed differently. It seems that older devices, such as my reader may have problems using those cards. This means I have to go buy a new reader tomorrow, I guess! Or be restricted to using only 1 Gig of the SD cards I use... Which is not a good idea for camera producing 37 MiB RAW files.
Update: My suspicion was correct. A new 10 € card reader solved the problem. The 2 GiB are back, I can read all the photos from the card.