Hi guys, There doesn't seem to be a lot of chat about this message on the Forum, so I'm posting a workaround for the issue. In my case I got the message "Unapproved caller. SecurityAgent may only be invoked by Apple software" when trying to boot from my CC Clone on the HDD in the optibay. I Googled the message and found a range of answers, including hardware fixes. But I was pretty sure, this wasn't a hardware problem. While this may not work for anyone with a single boot drive, it should work for anyone with a bootable backup. All I did was have CCC do a new clone, deleting all files not in original. Except I unticked the "var" folder. Now my MBP boots from the second HDD, with no issues. It's still a head scratcher, though.....as both my MBP & Mini will happily boot from the CCC on the external connected to the Mini.