My Civil War horror novel was chugging along nicely until about a week ago, when I got stuck on a chapter. I wasn't quite sure how to handle it and I'm still not. I stopped working on the novel for a few days, making the (valid) excuse that I had other things to do--edit the new magazine, write a couple of articles, research my next book proposal, etc. But I was really just stalling.
Then I asked myself, why aren't I writing? I already had several later chapters mapped out in my head, why wasn't I writing those? I had planned to write this book start to finish, because with my first novel I wrote whatever first came into my head, and had a hell of a time cobbling it all together. But with the present novel more than 80% done, what was I worrying about? So I skipped to the final two chapters and wrote them both. Now I'm trucking along fine and have written 4,000 words in the past two days, and I'm still doing all that other stuff I need to do.
Oh, haven't untangled that one troublesome chapter yet, but I'm working on it in the back of my head.
Sometimes you have to break your won writing rules to keep the momentum going. If a rule isn't helping you write, toss it out until it's useful again.