Need help with my R4

I'm recently having problems with my R4 in that most of the games that I have just downloaded and transferred into my Micro SD card doesn't work. They all say "could not read data, please turn off and reinsert DS Card" or something along the lines. It's not the download because the same files work on my brother's R4. Is this a known problem or should I just get a new Micro SD card?

Do games that used to work still work? What are the games that don't work? And your R4, is it an original, SDHC etc (what exactly does it say on the front of the card)? Also, what kind does your brother have?