From time to time, almost every academic gets behind on their work. If you've promised something to someone else (like a referee report, a chapter of a dissertation, or some work for a co-author) and you're past deadline, it's natural (wrong, but natural) to avoid the other person involved.
Of course, the later you get, the less you want to see the other person, and the higher the standard you hold yourself to (the "If I'm going to turn it in late, I'd better make it REALLY good" syndrome). Of course, this makes it more likely that you'll procrastinate. After a while, it spirals out of control, and you avoid the other person at all costs, sometimes to comical extremes.
Mary McKinney at Academic Coach has a great piece on this problem over at Inside Higher Education. It's titled Academic AWOL, and it should be required reading for doctoral students and junior faculty everywhere.