Create your own ISO

appletime wrote:

Using the USB Flash Drive/ISO install method for installing Windows on new Boot Camp partition.

In OS X, prepared the USB flash drive as <FAT32>, <Master Boot Record>.

In OS X, when you download the ISO file from Microsoft website, it is saved automatically in the Downloads folder. Do you copy and paste the contents of that downloads folder onto the USB flash drive? There is an error message stating it cannot copy All the files; is that okay?

2015 Macs (based on your signature) do not need an external installer. Please see https://help.apple.com/bootcamp/assistant/6.0/#/bcmp173b3bf2 . If you are manually building an installer, you will run into installation issues. Are you unable to install Windows without a flash drive? You should manually post the entire Downloads folder into the Flash drive, it may have more/larger files that a FAT32 USB can accommodate.

From Apple's website: Create an ISO image for Boot Camp from Windows installation media - Apple Support

Create your own ISO

Use these steps to make an ISO copy of your Windows DVD or USB flash drive:

4. Choose File > New Image, and then select your Windows DVD or flash drive from the submenu. [There are Three choices in New Image: 1) Blank Image, 2) Image from folder, 3) Image from "Untitled". Which do you choose?]

This is not required for your Mac. You already have an ISO from Microsoft. This is meant for Macs where the user has a physical DVD, but the Mac model does not have a built-in Optical drive.

BCA should prompt you for the ISO location (Documents is preferred over Downloads) and start downloading support software and start partitioning.

Please backup OS X , Windows and create a Windows System Restore point.