Excluded the whole Addon Manager, re ran the update and turned off the firewall and also excluded the Addon Manager from Windows defender. FSX will not start.
Doesn't happen here, and nobody else reported it. As I've said, the only possible reason for this is a mixup of files old and new, caused by the antivirus/firewall blocking some files and let pass others.
Be sure you disable AND configure to exclude the Addon Manager folder from ALL software that might interact on downloads: antivirus, firewall, anti-spyware, anti-spam, anything similar.
Some users don't even realize they are running more then one of such products that does similar things, which, in addition to unnecessarily slowing down the system, will require separate configurations so, if you excluded the Addon Manager folder in one software, it might still be blocked in another one.