32gb SanDisk Class 10 Corrupted Mess

I had posted here before about all my apps and games being deleted from my homepage and not being able to access the eshop. I finally figured out it was my sd card because I got a 4gb nintendo card and everything is running smoothly. Question is... WHY?! I bought the sandisk new, and each time i format it and redownload a game it will only last about a day before its useless. I check the files on my pc and they are just corrupted folders with chinese symbols everywhere. Then i had to reformat and try again. Ive lost 2 animal crossing saves during this time, and that hurts . What is causing this? is it the fact that is it a class 10 sd card? Or is it one of those 1 in a million chances where i get a defective sd card?