Ciao @cedrone
è necessario utilizzare un programma : minitool partizion wizard per 64Gb
For information : if you are using a 64Go SDCard, your formater software may force format in exFAT.
So if you have this problem, you can try minitool partition wizard (windows only)
http://www.partitionwizard.com/free-partition-manager.html
create as primary FAT32
ma vi consiglio di utilizzare 16GB con USB key 64GB or 128Gb
https://github.com/recalbox/recalbox-os/wiki/Use-an-external-usb-storage-device-on-recalbox-(EN)