Technically, it's not a block. It's more like, "I want to write this way, but the story's going that way, but I want to do it THIS way, but then I'd have to rewrite..." And no writing gets done.
Two things happen here.
1) I rewrite from the beginning. Complete restart. My first story, that got me writing? STILL working on it.
2) I suck it up and continue to write, in the way the story is already going. If I sit down long enough and pound keys, words will come.
This, at the moment, is about my first story. One day, I will leave it on the shelf. But it is not this day. Meanwhile, so I can say I wrote, I'm blogging and trying to figure out a First Draft for another story. I'm not restarting it. That's going to have to be a suck it up. First Story is the only one that gets re-starts and re-writes. Which, since the main character, plot, and world building have all changed, calling it First Story is something of a misnomer. I just used the same character names/personalities.