NDS: error!?!?

i have loaded some new games to my 2GB SD card and some of the new games aren't working... it said something like 'data could not be accessed, please turn off the power and reinsert the SD card'. i turned it off and reinserted the SD card again as instructed but still it didnt work :(

p.s. it's only the new games that arent working, all the old ones are still running okay!

does anyone know what the problem is???