If you use Windows Live Writer, most probably you also have twitter Notify plug-in installed. Don’t get surprised, as twitter notify plugin starts requesting for sign-in credentials from today and it doesn’t work even if you provide with username and password. That’s because twitter today has changed the way you sign-in to twitter. And it doesn’t notify that you needed to update.
Twitter Notify has been updated to work with Twitter's latest authentication changes by Live Writer team today . You have to just install it from Windows Live Gallery and it’ll start working again. You can get it from here.