In Terminal,
sudo -s,
enter password,
diskutil list,
find EFI disk #,
newfs_msdos -v EFI /dev/disk#s#
Erase and Format EFI partition under OS X
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In Terminal,
sudo -s,
enter password,
diskutil list,
find EFI disk #,
newfs_msdos -v EFI /dev/disk#s#