You and June seem to have sorted this out, Wendy. Just thought I'd tell you that it sounds as if you forgot to add your eggs. I'm pretty sure old baking powder would just prevent the bread from rising and wouldn't cause it to fall apart after baking.
Eggs are the binder in cakes and quick breads, and your result sounds as if the eggs were missing.

How do I know this? I once made oatmeal cookies that did the same thing... You guessed it... because I forgot to add the eggs! LOL