That is a very huge thing to forget... lol
When creating a Linux boot disk, it writes to sections of the media that identify it differently to the host. Some hosts can get past it, others, like V-Accordions, cannot. Basically, you need to reinitialize the USB stick and then format it again before it will work.
BTW, do NOT boot your V-Accordion with these USB sticks! Roland uses Linux as the OS and Linux commands to prepare the eeprom and then to upload and write firmware updates to the EEPROM. If you ever try this and by accident do the wrong thing, basically, the accordion is effectively killed and the only fix is to send it to Roland for a $2000 repair, if you ever want to use the accordion again, that is.