4 official 360 controllers, only 3 working in game

[hormel13]

Hey guys, I've got a pickle.  I have four official xbox 360 controllers.  Three are wireless, and one is wired.  I have the 360 controller driver installed.  When plugged in, they all get different player quadrants.  They are all recognized in the dolphin controller menu (both gamecube and emulated wii controllers).  For both Mario Kart and SSB, only the first three controllers work.  It doesn't matter which player quadrant the the wired controller has, and it doesn't matter what order the controllers are assigned in the dolphin controller menu.  Consistently, controllers 1-3 from the dolphin controller menu will work in game, and the fourth will not.  Any ideas of what could be causing this issue?