I must have tried it four times during the day today with different sticks, all other usb connected/disconnected etc etc, but it wont even flash a previous non modes bios from asus using the correct filename. Yet using EZflash in the same usb stick in the same slot with the same filename Z77ST.CAP slot it works fine although not with the modded bios. I was having a look at The Kings flashrom but that seems mega complicated.
I hope its not an RMA job as the worrying factor is I cannot flash any BIOS using the USB option, but it would be difficult to tell Asus here I want to load a modded BIOS, when the other options work fine.
Not the end of the world as Clover is working fine but of course Chameleon will not work with the unmodded BIOS, and its nice to have that "just in case".