Are you using an SD card while updating the firmware, how are you powering your board? Were you following this guide https://downloadmirror.intel.com/24748/eng/IntelGalileoFirmwareUpdaterUserGuide-1.0.4.pdf , at what point in this guide did you get that error?
I was using the Intel Galileo Board with an external power supply. I wasn't using the SD card. I was following the guide you mentioned.
I got this error when I clicked the "Update Firmware" button.
I tried it several times, reconnecting and turning the Galileo off and on, after 5 times it worked. No idea why.