I found this thread after having problems installing AccountEdge Plus v9 (2009) on a Macbook with a clean install of Mac OS X 10.11.1 (El Capitan). Running the installer I got to a certain point before I was greeted with a message that the software could not be installed because the software could not be found. I was puzzled. I have another 2 Macs quite happily running v9 on Mavericks and/or El Capitan, so I couldn't understand what the problem could be. It's pretty clear that the issue is nothing to do with Power PCs and Rosetta, since the software runs quite happily on those other Macs.
So, I tried control-clicking on the Installer to display the package contents. I navigated to Contents > Resources and found a load of packages for the individual optional installs. I located the program installer ('MYOB AE Plus App1230') and double-clicked it, which launched the installer for the program. I followed it through and the program installed fine, and seems to work perfectly.
It's worth noting that if you try to install any of the other optional packages, they wipe the contents of the MYOB folder in Applications, and replace with that part of the install. That's obviously no good, but as far as I can tell all the other usual MYOB folders can be moved from another Mac install. There are probably other ways around this minor hurdle.
So it seems there is some kind of compatibility issue between the MYOB *installer* and more recent Mac OSs, and not with MYOB itself. This is obviously good news!
Hopefully this issue is helpful to others
Thanks