I am having a problem very similar to what llamaaction described.
I have been using the 4GB workaround for several months without any significant issues. But yesterday, after downloading a song in RB2, the system indicated that there was no more space on the SD card. I figured no problem, I would just delete one of the dummy files I was using to pad the card. However, when I restarted RB2, it indicated that the SD card was unuseable, and that the SD mode was disabled. I figured that perhaps when it ran out of space during the download/transfer that something happened to make the card unreadable. I have tried low level formatting with SDFormatter numerous times, with no luck. The Wii itself is fine with the card and can read and transfer information to it. But RB2 won't, even when there is less than 1.99 GB free.
Any suggestions?
TIA