I'm not sure that that's the case, but if the limitations are the same as for the internal SD card, then you need to format it to regular FAT. I used Guiformat fom Ridgecrop (can't post links because I'm a newbie, so just google Guiformat).
I've never heared of the tool before, but it came up when I was looking for a utility that could make 64GB FAT volumes and it worked fine.