I have the feeling it wasn't Dacey's Dream that was so difficult after all. I'm having the same trouble with Muse. Barely 500 words now, and just a little over 1000 for the day so far. I really do need to get my brain kicked into gear, but I suspect it's not going to happen tonight.
I never like nights like this. I have the story. I have a funny scene coming up. I just can't... get there. I can get a half dozen words at a time, and then it's like I have to stop and think the entire process out again. Far better on the days when it flows, of course... but you can't have that every day. And if you wait for them, well they're harder to pull up.
I'm going for a few hundred more words. If the writing part of my brain has not kicked by then, I'll call it a night.