OK, it seems the problem was the SD card. I tried a different one and it works fine.
Now the problem I'm having is that the reader has died on me twice. Nate at the Digital Reader has experienced the same thing. The battery had nearly a full charge and when I went to wake the reader up after it had been asleep for just a few minutes I got nothing. The first time it happened I put it back on the charger for a few hours and it started working again. This time I've had no luck reviving it so far. Anyone else experienced this?