We have two XBEE PRO S1 devices paired and communicating. Something occurs that causes one of them to stop receiving and sending. No response to incoming data and no response to commands from the microcontroller it is connected to. One device is in API mode, although we have seen either one stop talking. A hard reset is required to start it up again. Inside of the normal operating parameters of the device, what can cause this? If there are conditions where this can happen, are there standard configurations or precautions to avoid this?