boot camp fails to copy windows 8 installation files
Have you tried to use a different flash drive? I have had issues particularly with SanDisk Cruzer flash drive that are unable to be used as boot devices because of the firmware on the flash drive. Try a different flash drive and see if you have the same result. I have an 8 GB Sony flash drive and a 4 GB Kingston flash drive that have never failed as bootable USB devices. Using the same process, I just could never get the SanDisk to work.

Otherwise burn the ISO to a DVD and and Bootcamp should be able to find it just fine.