Xbox 360 controller vibration in build?

I'm using XInput for vibration can't get the controller to vibrate for a windows executable build of game we're working on. I know the XInputInterface.dll file has to be in the root folder with the .exe file, but that doesn't help.

The code for detecting controller:

  PlayerIndex testPlayerIndex = (PlayerIndex)i;
  GamePadState testState = GamePad.GetState(testPlayerIndex);
  if (testState.IsConnected)
  {
                                                connected = true;
      playerIndex = testPlayerIndex;
      playerIndexSet = true;
  }

The problem seems to be that testState.IsConnected is never triggered; the build never detects that a controller is detected. I tried using Input.GetJoystickNames as well, but that never detects the controller either.

This all works like a charm in the editor, but doesn't work at all in the build (although the controller itself works fine with the game). What's wrong?