help with my R4!

hi all, i was wondering if anyone out there could help me out. just recently, all the roms that i've been downloading hasnt worked on my r4. everytime i try to play a game, it says "Could not read data. Please turn off the power and insert the DS card". it didnt do that before, and also, the games that i had from a while back still work, its just the new ones i just downloaded recently. So if anyone knows what the problems could you please help me?
thanks in advance

Please post in the appropriate section when requesting help next time. Moved.Also, please read the Common Issues thread as well, it clearly states how to fix this problem.