I had the error as the updater started, had to uninstall my AV and Firewall as wel as disable the Win firewall to get it going took 36 hours to solve....
Risky move considering all of the D3 accounts being hacked at the moment.
When an anti-piracy method is affecting the game for people who legitimately bought it and causing other people not to buy the game, there is obviously something wrong with it!