Thank you, this was exactly the problem. I forgot everything must be on FAT32 to work on the Pi. I used the Disk utility on my Mac to format and now everything works fine.
Mine was detected by windows as 64gb too, and i can used it, but when recalbox tried to format it on ext, there was on error. These fake SD are detected as 64gb but only 7 or 8 gb are available.
