Just reporting that I too encountered the message "Only a single instance of Hero Lab can be used at a time prior to licensing" when upgrading. The symptoms (and resolution) went like so:
- Opened Hero Lab 8.8 (32-bit).
- Used the updater to download Hero Lab 8.9.
- Updater asked to exit HL 8.8 in order to Install 8.9. Said yes.
- HL 8.9 installer ran and asked if I'd like to restart HL now? Said yes.
- HL 8.9 (32-bit) started.
- Got the error message "Only a single instance etc." This was slightly puzzling, because I only had one instance running.
- Reactivated the existing license (HL 8.9 32-bit).
- Exited.
- Started HL 8.9 64-bit.
- Got the license activation dialog again, and also the "Only a single instance" message.
- Reactivated the existing license (HL 8.9 64-bit).
- Everything works.
So the trick is that Hero Lab wants you to activate your license separately for both 32-bit and 64-bit copies. When you're upgrading, it automatically starts the 32-bit version first because you were updating from the 32-bit version, so you may as well do that one first, exit, then do the 64-bit one.
Once you've reactivated the license for both processor architectures, everything works fine.
I'm excited to see if I'll be able to compile custom scripts more than one time without restarting Hero Lab using the 64-bit version. That's been a pain in the butt for ages, and my understanding was that it was a memory issue. Hopefully with the 64-bit upgrade HL will be able to address a much larger memory space.