for some reason they have included the sd firmware update twice, what your going to have todo is download vers 27 again, restart in gba mode (remove your passcard) and do the update to 27 in gba mode.
edit:- ps i did the same lol
do you not have to hold select down to get to original ds screen andthen select gba mode from there?
do you not have to hold select down to get to original ds screen andthen select gba mode from there?