*Finally* after trying hundreds of things to fix this problem, I found a fix for the same error on a different software product:
Create another account with Administrator privileges. Log into that account. Install the software. It worked like a champ. I can only image that my original account 's Registry permissions had changed somehow too complex to try to fix with setacl or other cryptic Windows 7 utilities.
Right now I’m trying to copy the user profile from my original account to my new account on Win 7x64. You have to use Windows Enabler “on” to be able to copy anything other than the default profile, but even if it doeesn’t work, worse case I’ll have to set the wallpaper and desktop icons up again. Bugger, bugger, bugger.
IMHO EndNote Tech Support should have suggested this simple fix instead of “disable your antivirus.”