I have a Panasonic bread maker that made excellent French bread in the Colorado Rockies. However, since moving to sea level in the Pacific Northwest, the same breadmaker using the same ingredients just doesn't work -- the dough doesn't rise and the bread comes out heavy as a brick. What gives?
You may need to play around with the amount of yeast until you hit the sweet spot.
I hope others will come in with more suggestions as this was the only thing I could think of.