Well, not actually blocked (unlike this doorway), but it was a sticky day, and this works very well as a visual metaphor. It was one of those days when one's research and ideas seem like dull sawdust; or, to be more specific, when I felt like the contents of an as-yet-unwritten-though-I-know-what-it-looks-like-in-outline chapters seemed dull and descriptive.
So ... why is it that it's so hard to unblock? If I were a domestic drain, I'd swallow vinegar and baking soda: I know perfectly well that the writerly equivalent for me (if no shower is to hand) is to go outside, go for a walk, change pace, change scene, change (which doesn't mean "sit on office floor and investigate what papers one's forgotten about in cupboard."). And indeed, as soon as I gave up, around 6 p.m., and headed through the pine-tree smelling car park, it became instantly clear to me what I could move from the (equally unwritten) next chapter, and made an effective - I hope - hinge.
I note the blocked doorway has no hinges, and will try not to see this as a further, and grim visually articulated message.