C. Nathan Gunn
We all have periods when it's difficult to come up with something. Generally, for me, it tends to be the minor plot elements and incidental sequences.
I'm also a good top down thinker, so when I have a big idea, I run with it and as I said above, filling in the small spaces can be hard.
I tend to schedule myself time to sit down and write when I find myself in those spots. Committing to it can help force me to get something down that I can always go back and edit, if I get some inspiration later.