to fix this all you need to do is go into the menu (with out the r4card in the ds) and change the date back a couple of years or more .then u will be able to load up the r4 again.on the 15th of april all r4s stopped workin because of this error so all u have to do is trick the ds into thinking the 15th of april hasnt come yet and ul be able to play.
hope i helped!!