Recently i was trying to install windows 7 using boot-able flash drive but after booting i was stuck on this error (Load Driver: A Required CD/DVD Drive Device is Missing).. i checked everything is fine with BIOS settings and hard drive is showing properly.. So I did some research and found
that windows 7 will not deduct drivers if the USB is plugged in 3.0 USB port. So the solution is very simple to solve the issue I had to plug in boot-able USB device into 2.0 USB port. So i just removed boot-able flash drive from 3.0 and plugged into USB 2.0. then i just reboot system and chose flash drive as first boot device. So now i am able to run setup without any error.
I hope this short article will help some users facing same windows 7 load driver issues (A required cd/dvd driver is missing usb) during installation.