im have a same error on gigabyte ga-z77-d3h always wen boot the chimera bootloader write in screen 4 times the error message "EBIOS read error: Error 0x31. Block 0x0 Sectors 0"
this error its generated when the bootloader try to read the internal memory card (conected at internal usb port) as if it was a disc in here
4 errors for 4 port
im try to
a) disconect the card, boot and no error ---> work, but not valid workaround if im like to use memory card
b) disable on bios the "support legacy usb" ---> work, but not valid workaround if im like to use keyboard usb to intercept boot to select options or different partition to boot
c) in uefi bios of the z77 im found in advanced mode, in tab peripherals well down a option to configure how its treated the usb devices conected to the motherboard.
by default alll figure as auto
the card appear as "Generic Storage Device 0.00" and i set to FDD or CDROM type , save and reboot
voila no more error message "EBIOS read error: Error 0x31. Block 0x0 Sectors 0"