Bee
My S3 did not recognize card when it was formatted exFAT.  S3 seems to have problem supporting exFAT format in higher capacity like 32gb or 64gb.When I inserted the SD card, it just kept saying that SD card was "damaged" and I just got stuck on "Unmounting SD card" screen when I tried to format it on my phone.I just manually formatted the SD card to FAT32 in Windows 8 and inserted it into my phone.It runs smooth now.  Seems like a lot of people are having trouble to get the SanDisk 64gb to work in S3.  Hope this helps.