Gina, I think your problem is too much moisture. I've read this in a
bread book I have laying around in some pile.
Anyway, I've had this problem recently in my 3 year-old Hitachi. It
happens even when I cut the water level down to 250mls from 270 for a
large loaf. I suspect is has to do with the high humidity in
Bloomington. However, the fact that my roommates keep a fan pointed
into the kitchen (blows air conditioned air in there) might have some
influence as well.
The Internet: Your old grade school home room.