I wouldn't say I get blocked, exactly. Sometimes it feels too hard and I procrastinate. I tend to feel that way in the early stages of writing, before I really know my characters. I'm fumbling around at that point and it's tricky. But the solution to that is to put my butt in the chair and write, even if I'm writing drivel. You need to get the juices flowing. Later in a story I sometimes lose my way and feel like I've gone off track. When that happens I go back to the beginning and read all the way through again. That usually sets me straight.