We apologize for the errors that have occurred in the latest Mac installation. We are tracking down the source of the issue now and hope to have a solution soon, but don't have a good ETA quite yet. I would expect that this will be fixed before the end of the week.
The source of the problem seems to be a conflict with Apple's Gatekeeper which aims to prevent things downloaded from the internet unless certain criteria are met. We believe we are satisfying those criteria, but the error persists, so we are still investigating.
For those looking to revert back to 32-bit until we get this fixed, you can find previous updates you have downloaded by going to finder, hit Shift-Cmd-G to go to a specific folder, and type in: ~/Library/Application Support/Hero Lab/download. This folder contains items previously downloaded by Hero lab, including previous installers, which are named hl<version>_mac.install.dmg.
Woohoo! That worked great! 8.8 here I come. Shows how little I know about my own Mac.