Why Can't I Load Kali Linux?

I downloaded the ISO of Kali Linux 2016.1 and put it onto a USB Drive using first Win32 Imager, then Universal USB Imager (UUI). I then tried to boot my system from the USB Drive (A 16GB SanDisk Cruzer) 3 steps into the setup process, it said "Unable to find CD-ROM. Retry?" I re-inserted the USB and tried again. Same message. Any suggestions?