Hello
It's a common problem with laptops. The thing is each Kinect should be connected to a separate USB controller. Often in laptops all available USB ports are linked with the same controller, and another is used for internal components like docking station connector.
Try all possible USB ports combinations. If this does not work, then you'll need an external ExpressCard USB controller similar to
this one, if your laptop has the ExpressCard slot. If not, then I cannot propose any solution besides using another computer - either a laptop with an ExpressCard slot, or a desktop.