Problem
You get the following error when adding a boot image to SCCM 2012 R2
“You cannot import this boot image. Only finalized boot images are supported.”
Solution
Check if you have McAfee VirusScan Enterprise installed on your SCCM server.
If yes, make sure you have these exclusions configured. In my case, I also had to temporarily un-install McAfee VirusScan.