Ok so I have a good .iso file of windows 7 that I want to use to put windows 7 on a 2011 Macbook Pro 8,1. I have used this .iso file before and it works great. I used this file to put windows 7 on my own MacBook Pro 8,1. I hacked the Boot Camp Assistant to help me make a bootable USB on my non-retina Macbook Pro and used this method with great success making a bootable USB to install on a MacBook Pro Retina in Boot Camp. Virtualbox will not boot from the USB and I cannot figure out why! This is supposed to be a bootable USB.