After working with Support, I eventually got it installed - what I had to do was uninstall using the ESET uninstaller as shown in the KB guide. Afterwards I reinstalled using the Live installer, not the offline one. I tried using the offline installer first to save myself a download, but that failed as usual - I reran the uninstaller and tried the live installer, and this time it worked properly.
I don't know if it's the going to be the same fix, but you may as well try and see if it helps your issue.
