After a few days playing without problem, the same error happend to me today.
I logged off yesterday, turned off my computer and today couldn't log in.
I haven't installed anything since WoW, spotify, discord and avast.
I saw the programs running and there was a "Install Shield Update" that's from Windows 10.
I ended it's process and removed completely from my computer. I tried again and it worked.
Maybe that was the problem the whole time. Just sharing here my solution, since it might help someone else.
Thank you again Naozxy!