I ran the uninstaller, which worked fine, restarted and downloaded the 1.12 installer from the link you provided but I'm getting the same error. After I tried installing v1.12 a couple of times I ran the 1.11 installer, which I still had on my machine, just to see what would happen, and it ran correctly.
I've quit all other applications while installing and repaired disk permissions - no change. The installer gets to the "upgrade" button. After I hit the button it displays "preparing target disk", then very briefly something about "preparing vienna instruments" before giving the message "Please try installing again".
Hopefully the information that 1.11 works and 1.12 doesn't will provide some clue.