Hi Mike,
I have exactly the same problem. I have a 16Gb Trancend Class 2 uSD card (and 16Gb Fuze+) which can be read and written over USB by the player itself. Due to that I came to the conlusion that player and SD card are ok but the firmware of the player is buggy.
Some time ago I wrote some firmware for SD card access on ARM controllers. Stuff like USB MSC you got out of the box. No talent needed but to use an SD card in your own application is much more difficult. Different SD card have different timeouts - unluckily SD card specification doesn’t specify how to handle this in a proper way.
