Morning AoX, everything good at your end?
Historically, MC and AV software in general have such a bad relationship that I've found I get the best performance by excluding the entire JRiver program files directory, and the entire JRiver appdata directory in my AV software's real time scanner options.
During install, everything is first unpacked to a temp folder, so if in the extremely unlikely event that an infected installer was released, that would be caught during extraction.
I find highly unlikely that anything would get through the first lines of defence here and then hide out in the relative safety of my MC folders, and all firewall rules for MC are ip specific, so if it asks to go somewhere unauthorised, it can't. I reckon I'm covered.
If you are not comfortable using such exclusion rules, I'm willing to bet that the reason it's failing is because your AV software is trying to scan the zip file while it's in the process of being created and 'filled'. If I'm right, then adding the library backups folder to the AV exclusion list will fix your problem... worth trying?
-marko