I often find that my block caused by resisting the story. Like, the story may be telling me where to go, and I think "Nah. that can't be right. Let me think about this some more." And so on. When I surrender to the story, the writing comes back.

So, the story is telling itself, and I just have to listen to it. I dunno how many times that's happened, sometimes for days on end, and when I finally give in, the writing flows.