Mac Models prior to Late 2013 models are preUEFI models and do not properly support EFI Boot for Windows. BCA will not recognize a USB containing Windows installation media. You can use your W10 Product Key to download an ISO to the Mac directly from -us/software-download/home . Do not use a mixed 32-bit/64-bit ISO, it will not work. Download a 64-bit only ISO and use BCA.