Hi. i found that on mine when I owned a 708 that the only sd card that I could copy and get to work was a 4gb sd card. I tried them all but for some people have success with bigger sd cards
Now, I transfered my old sd card from 4 gigabytes data to new sd card 16 gigabytes. I got it, my maxidas ds708 it recognize the new sd card (16 gigabytes) and I updated it.