You must format the cards to FAT32 as the xtra drive instruction say. Difficult to do with a Windows computer, use freeware Macrorit NTSF to FAT32 Converter. Now it works with a 64 GB card. Update- increasing rating to 4 stars since this has become my favorite way to transfer files from my GoPro to my iPhone and iPad for editing and then to the computer. However, I can't get AirPlay to work with Apple TV from files on the drive, and it lacks thumbnail views on the iPhone and iPad.