I've been having problems with the 2.1 installer.
Not your issue, mine would pretend that it was installing 2.0 despite that I clearly downloaded 2.1. See this thread:
https://www.mobileread.com/forums/sho...40#post2909840
How I resolved the issue is to use a vpn to download the current installer and that installed properly.
If that's outside your area of technical proficiency you can download the 2.0 installer from here:
http://download.calibre-ebook.com/2....4bit-2.0.0.msi
2.0 works fine.