Win8 downgrade - Windows 7 installation "Driver not found" [duplicate]
This message happens when you try to install Windows 7 via USB flash drive and use the USB device on a USb 3.0 port. Windows 7 doesn't support USb 3.0 out of the box, so you must inject the USB 3.0 drivers into the Boot.wim with DISM first.
dism /mount-wim /wimfile:boot.wim /index:2 /mountdir:mount
dism /image:mount /add-driver:"usb3" /recurse
dism /unmount-wim /mountdir:mount /commit
Now copy the modified boot.wim to the flash drive.