Launch turtlebot_world.launch failed,can't spawn turtlebot model

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[ERROR] [1509691216.710669237]: Skipping XML Document "/opt/ros/indigo/share/gmapping/nodelet_plugins.xml" which had no Root Element.  This likely means the XML is malformed or missing.
[ERROR] [1509691216.711609615]: Skipping XML Document "/opt/ros/indigo/share/gmapping/nodelet_plugins.xml" which had no Root Element.  This likely means the XML is malformed or missing.

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[spawn_turtlebot_model-3] process has died [pid 6095, exit code 1, cmd /opt/ros/indigo/lib/gazebo_ros/spawn_model -unpause -urdf -param robot_description -model mobile_base __name:=spawn_turtlebot_model __log:=/home/dclab222/.ros/log/4394944c-c05c-11e7-b25e-94de80ac314e/spawn_turtlebot_model-3.log].
log file: /home/dclab222/.ros/log/4394944c-c05c-11e7-b25e-94de80ac314e/spawn_turtlebot_model-3*.log

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When I launch turtlebot_gazebo turtlebot_world.luanch. It's would An error occurred.

I have reinstalled ALL ROS ,

I can't spawn turtlebot model, where is wrong QAQ