Hi,
my son updated his dsi yesterday and he has the same problem, it was working fine until he updated his dsi, now he gets an error message when he tries to play the r4 card, his card works on his brothers dsi so we tried his brothers card on his dsi, same problem, it wont work so it looks like updating the firmware on your dsi will stop your r4 card from working !!! Did you end up sorting it out ?? I have spent most of the day trying to find a solution on the net and have come up with nothing. As stated, his r4 card is fine because it works on his brothers dsi, this is sooooooooo damn frustrating !! If there is anyone who reads this and know a solution could they "PLEASE" let me know wot I can do to get this working ... I tried formatting his r4 card and d/loading the updates suggested but that didnt work either !!