Comments + Twitter Sign In Not Working

I'm in the process of setting up Comments+, and so far, the Facebook & Google sign-ins work. But for some reason, when I click the Twitter sign-in, it opens the app window and it shows a 404 error page with the url of the current page/post and /false appended to the end.

I know I have the correct API information entered, and I even tried regenerating the API keys. Any ideas on how to get this working?