15" rMBP & Windows 7 Bootcamp--Won't boot from USB

I created a USB install drive using the Bootcamp software on my early 2013 15" rMBP running 10.8.4. Created it from a Windows 7 Pro 64-bit ISO downloaded from Digital River (microsoft official distribution source, ISO X17-59186). The drive is USB3. When bootcamp finished and the computer restarted, it goes to a black screen with PC-style text saying

there is no bootable device inserted, please insert and press any key

My USB drive is of course inserted. I selected all the options at the start of bootcamp and it put its drivers on the same USB drive. What is going on here and how do I install Win7 from USB?

Source: http://forums.macrumors.com/showthread.php?t=1606909&goto=newpost

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