If you're using a mac, the USB drive will have hidden extensions as part of Spotlight, etc. Easy fix is to not use a mac. If you use a mac, download the file to your usb, then insert it in a windows pc. Enable hidden folders and delete all folders except your update. or you can get really technical on a mac. Put the update on the usb, then run terminal:
Open Terminal, type:
cd /Volumes/<your thumb drive>
then type:
rm -rf ._.Trashes .Trashes/ .Spotlight-V100/ .fseventsd/
Then eject the disk. You should now have ONLY the firmware folder on it.
