We had a new wide plank mahogany hardwood floor installed (floating with grooved planks fitting together). It was also nailed in places. We came back from 2 weeks away in August and found the floor had "tented" (2 boards risen up in a tent about 3 inches high) and about one quarter of the floor had cupping. There was no moisture dropped on floor and the construction person doesn't know what caused this or what to do now!

Oh I am pretty sure he knows what caused it and how to fix it, he just doesn't want to eat the project. It tented because the wood was not acclimated properly and you do not nail a floating floor. Your wood was dry and installed tight. It has now absorbed humidity and expanded. Due to the nailing it has no place to go but up, he screwed up. Click on the next word Google (http://www.google.com/#q=how+to+install+a+floating+floor&hl=en&prmd=iv&source=univ&tbs=vid:1&tbo=u&ei=DmeRTP2UBIH88Aar8Z3ZBQ&sa=X&oi=video_result_group&ct=title&resnum=2&ved=0CCIQqwQwAQ&fp=a7dbfbf4b55adffd)

Do you have a full basement, or crawlspace, or is this floor on a concrete slab?
You could have serious moisture below the floor, from general dampness or visible water.
I once lived in an old apartment building with solid oak floors that tented because of a very tiny leak in a water pipe spraying a fine mist upwards.