On another note, David, I believe the reason REX insists that antivirus must be switched off before install is that the Rexinstaller.exe file conains the virus W32/Mickey.Z.gen!Eldorado, discovered during a routine iolo System Mechanic 2018 scan. What it's doing there is a question that only REX can answer. The following is what I discovered about it (describing Q and not Z, but it's the same virus underneath.) This hasn't been edited. Needless to say I have quarantined it and deleted it.
"W32/Mikey.Q.gen!Eldorado is a virus detected by Microsoft Windows and several Antivirus or Anti-Malware software vendors. This W32/Mikey.Q.gen!Eldorado threat is classified as PUP a Potentially Unwanted Program or PUA a Potentially Unwanted Programs because it inflicts and acts as a malicious threat into your Windows XP, Windows Vista, Windows 7, Windows 8 or Windows 10 computer system.
W32/Mikey.Q.gen!Eldorado modifies system files, add’s new folders, creates Windows tasks and might shows advertisements on your computer and browser.
W32/Mikey.Q.gen!Eldorado is adware which is bundled using custom installers and dropped on your computer during the installation process. Most users have no idea how this W32/Mikey.Q.gen!Eldorado threat is installed on there computer and what it is, until their Antivirus or Anti-Malware software detects it as a malicious threat or virus."
I definitely want to know what REX has to say about it.