Hi Lar,
I had the same problem but i was using a different datalogger. I have been told to change the SD card and I did but it didn't work. Eventually I found out that the problem was with the soldering. I bought a new datalogger and it worked.
In your case:
1- Double check that you are using the correct Chipselect pin.
2- Try to get a new SD card.
3- Check your soldering.