Failed to detect objects with UP AI Core X

I am using UP AI Core X on Ubuntu 16.04. https://up-board.org/ai-core-x/

I use the latest version of OpenVINO toolkit(2019.1.133) to detect objects from the webcam.

But I sometimes get these error messages:
1.

E: [ncAPI] [    183032] ncDeviceOpen:799    Failed connection to device (3.1-ma2480) with error 5

2. Traceback (most recent call last):
     File "/usr/lib/python3.5/threading.py", line 914, in _bootstrap_inner
       self.run()
     File "/home/tk/DeliveryVan/openvino_inference/obstacle_detect.py", line 50, in run
       detector = ObjectDetect(detect_model=detect_model, detect_mode=detect_mode, confidence=detect_thresh)
     File "/home/tk/DeliveryVan/openvino_inference/object_detect.py", line 33, in __init__
       detector = OpenVinoDetectSSDInceptionV2(threshold=confidence)
     File "/home/tk/DeliveryVan/openvino_inference/openvino_detect_ssd_inception_v2.py", line 23, in __init__
       self.exec_net = self.plugin.load(network=net, num_requests=2)
     File "ie_api.pyx", line 395, in openvino.inference_engine.ie_api.IEPlugin.load
     File "ie_api.pyx", line 406, in openvino.inference_engine.ie_api.IEPlugin.load
   RuntimeError: Can not init USB device: NC_ERROR
   

3.

E: [xLink] [    973107] dispatcherEventReceive:368      dispatcherEventReceive() Read failed -4 | event 0x7f38f2339ee0 XLINK_READ_REL_REQ

E: [xLink] [    973107] eventReader:230 eventReader stopped
E: [xLink] [    973107] XLinkReadDataWithTimeOut:1377   Event data is invalid
E: [ncAPI] [    973107] ncFifoReadElem:3313     Packet reading is failed.
E: [watchdog] [    973222] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    974221] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    975220] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    976219] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    977219] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    978218] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    979217] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    980216] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    981215] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    982214] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    983218] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    984217] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    985217] sendPingMessage:132  Failed send ping message: X_LINK_ERROR
E: [watchdog] [    985217] watchdog_routine:327 [0x7f38ec08bbe0] device, not respond, removing from watchdog

Any idea?