Weird Guppy Disease

I've bought some guppies from my LPS but a lot of them are dying with a weird, dropsy like disease. The symptom are as followed:

First, the fish gets a white, vertical band-like marking on the body.
Second, the scales on the white band flips up just like dropsy.
then thes fish suddenly jerks and goes unconcious, eventually dies.

Anyone know what kind of this disease/infection this is? Any help greatly appreciated!

Unlimitedfishboy