I'm getting this error on my mid '11 Mac Mini (running OS X El Capitan 10.11.6) when I'm trying to install an audio plug-in by Presonus, the demo of OrangeVocoder 10th Anniversary Edition. The software manufacturer is in Germany and this is just the demo, so I doubt they will be much help. The first thing I tried was downloading a new copy of the DMG file, but it gave the same error when I attempted to install.
I believe the problem is because I had this installed previously, but I recently uninstalled it. After reading this Apple thread I opened the .MPK file (Show Contents) and copied the contents to the desktop and tried to install from there, but got the same error. I also used Terminal and navigated to /private/var/db/receipts and deleted two .plist files that referenced the software. Lastly, I tried this command to disable code-signing check, but it didn't help either: defaults write com.apple.frameworks.diskimages skip-verify -bool true
Worth noting that the DMG is not signed (I checked with terminal command codesign -dv path\ to\ DMG) but the DMG does indeed pass image verification in Disk Utility.
At this point I am out of ideas, but I really need this plug-in for a project I'm working on. Any help greatly appreciated. Thank you.