KORG ESX-1SD says “No Files Error” when loading samples

I’m using a HAMA 2GB Class 4 SD card.

The card works fine — I can format it on the ESX, save the current ESX data to it, and load that data back successfully.

But when I put a 44.1kHz/16-bit WAV on the card and try to load it, I get “No Files Error.”

Any help appreciated!