Just to update, here's what I did after the error message above.

I closed the little MyPoints pop-up screen.
I backspaced on the survey screen and got to the last page (where you check off what movies you own).

I clicked on 'submit' again and this time the MyPoints, "Congratulations! You just earned 100 Points" pop-up message appeared.

I clicked on "continue to MyPoints" just to make sure that it knew indeed who I was (remember that the original error message appeared after I tried to sign-in by entering username and password), so something must have gotten through.

Great.