Not enough power! These things should power 6 miners with 3A of power, but for whatever reason, they aren't. I found a way to hook them up so they all run. The first usb hub can give the other 2 a little extra juice if you use the labeled charging ports to bridge the other hubs off of.

SCOTTY, WE NEED MORE POWER!
I'M GIVIN' HER ALL SHE'S GOT CAPTAIN!

http://i43.tinypic.com/5ybxab.jpg