Starting in 2001, the US started import drywall from china. I guess it really hit hard after all the hurricanes and what not hit Florida. Anyways Chinese drywall gives off this horrible smell (like rotten eggs) when it gets hot and humid. It also gives off other gases which lead to breathing problems, cancers, and a bunch of other crap.
To correct the problems all the drywall, a/c, electric, plumbing needs to be replaced.