Indeed, the most common cause of such symptoms is that both Kinects are on the same USB controller.
If you insist that you have tried all possible combinations of USB ports then there should be some other reason.
However, let's check the picture in Device Manager. Connect one sensor to front USB port, and other to back USB port (usually front ports are connected to a different controller than the back ones). Open Device Manager, locate Kinect devices and see whether they have any problems reported. Then switch to 'Devices by connection' view, and again locate both Kinects by expanding the tree. See whether they are under the same USB controller node or different ones. Attach screenshots here, if you find it appropriate.
Also you can provide us a trace log from iPi Recorder. Open the program, wait for it to refresh the device list, then press
tools > show trace in the top-right.
Recently, we've been reported of Kinect for XBOX malfunction on Windows 8.1 after one of the OS updates.
http://forum.ipisoft.com/viewtopic.php?f=5&t=9148But from the screenshots it looks that your OS is Windows 7, that's right?