Just now, I was getting this error whenever I tried to view a question or go to ask a question here to complain that I couldn't view questions:
I also saw this in an incognito window, where I wouldn't be logged in.
I was however, able to post an answer (and possibly a comment) on a page I already had loaded when this was happening. Fortunately, the system prevented me from posting duplicate answers.
So I'm reporting that this happened.