Windows 8.1, BootCamp does not find the ISO image.

When I try to install Windows 8.1, BootCamp does not find the ISO image.

1. I purchased Windows 8.1 Pro, I downloaded the .exe requested file from a Windows computer, performed the steps recommended by Microsoft in order to create the ISO file saving it on a flash drive as well and, as a precaution, on a DVD too.
2. I performed the "Download the latest Windows Support Software from Apple" step directly into another flash drive and having it completed BootCamp displays the following message:
   "The installer disc could not be found – Insert the Windows installer disc and wait a few seconds for the disc to be recognized. "
3. So happens that I have tried this using the DVD, pendrive and also copying the ISO file to the desktop and to the "Documents" folder as recommended in certain websites, but none of this has made the process go ahead. What can I do?

My equipment is a mid 2011 iMac running Mac OSX 10.10.1.