Hello,
When I was trying to flash the SD card with my usb card reader it wasn't working, (the same problem you describe). when I've tried with my wife's laptop that has build in memory card slot it worked fine.
Also I've read somewhere the SD card should be small in capacity.
I don't know if this helps.
Thanks for the Info.
I also get some Infos from Allex. He said that you have to take an real SD Card and not an Micro SD with an SD Adapter.