ERROR : cannot identify

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Hello. I input 'roslaunch elp_stereo_camera elp_stereo_camera.launch' and I got an error as below.

ubuntu@ubuntu:~$ roslaunch elp_stereo_camera elp_stereo_camera.launch
... logging to /home/ubuntu/.ros/log/7b619c30-e2fe-11e6-9f1e-0022cffa2d4b/roslaunch-ubuntu-4255.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.

started roslaunch server http://ubuntu:41191/

SUMMARY
========

PARAMETERS

 * /elp/left/camera_frame_id: elp_left_optical_...
 * /elp/left/camera_info_url: package://elp_ste...
 * /elp/left/camera_name: elp_left
 * /elp/left/framerate: 15
 * /elp/left/image_height: 720
 * /elp/left/image_width: 1280
 * /elp/left/pixel_format: mjpeg
 * /elp/left/video_device: /dev/elp_left
 * /elp/right/camera_frame_id: elp_right_optical...
 * /elp/right/camera_info_url: package://elp_ste...
 * /elp/right/camera_name: elp_right
 * /elp/right/framerate: 15
 * /elp/right/image_height: 720
 * /elp/right/image_width: 1280
 * /elp/right/pixel_format: mjpeg
 * /elp/right/video_device: /dev/elp_right
 * /rosdistro: indigo
 * /rosversion: 1.11.20

NODES

  /elp/
    left (usb_cam/usb_cam_node)
    right (usb_cam/usb_cam_node)

ROS_MASTER_URI=http://localhost:11311

core service [/rosout] found
process[elp/left-1]: started with pid [4273]
process[elp/right-2]: started with pid [4274]

[ERROR] [1485349340.027221093]: Cannot identify '/dev/elp_left': 2, No such file or directory
[elp/left-1] process has died [pid 4273, exit code 1, cmd /opt/ros/indigo/lib/usb_cam/usb_cam_node __name:=left __log:=/home/ubuntu/.ros/log/7b619c30-e2fe-11e6-9f1e-0022cffa2d4b/elp-left-1.log].
log file: /home/ubuntu/.ros/log/7b619c30-e2fe-11e6-9f1e-0022cffa2d4b/elp-left-1*.log

[elp/left-1] restarting process

Please help me..