I looked in two of the manuals from my now defunct machines and they both suggest that the loaf has overrisen or risen too fast.  They suggest further that the yeast and/or water be decreased.  Also more salt could be added.  Salt inhibits rising or slows it down, so that makes sense.  And clearly less yeast would work.  I would try one of those suggestions and see how it works for you.  I hope this helps.

Marni

Sounds like your recipe, if you're using one, is out of whack.  Try Googleing "Bread Machine Recipes".  There's loads of them out there.  Here's a link I found using Goodle but, as I said there's a ton of bread machine recipes out there.

http://allrecipes.com/Recipes/Bread/Bread-Machine/Main.aspx

Howard - St. Augustine, FL

 I had the same thing happening to me (in a 2-lb machine, using 1 or 1.-lb recipes). I found the answer to my problem on the King Arthur Flour website: http://www.kingarthurflour.com/tips/bread-machine-basics.html

Look at the hint#9

"Bread that rises, then collapses in the middle as it bakes -- the infamous “crater bread” -- contains too much liquid. Adjust your formula."

That's what I did and I didn't have a problem anymore :)