roslaunch error [gazebo-1] process has died

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Hello guys, I'm following this tutorial on gazebo 1.9 http://gazebosim.org/wiki/Tutorials/1.9/ROSMotorandSensorPlugins but when I type: roslaunch rrbotgazebo rrbotworld.launch

it gives me this error

Msg Connected to gazebo master @ http://127.0.0.1:11345
Msg Publicized address: 172.20.242.19
[INFO] [WallTime: 1398703874.946736] [0.207000] Spawn status: SpawnModel: Successfully spawned model
[urdf_spawner-3] process has finished cleanly
log file: /home/a2ur4/.ros/log/7e4dd822-cef3-11e3-85cd-001bb1f663f3/urdf_spawner-3*.log
Segmentation fault (core dumped)
[gazebo-1] process has died [pid 21117, exit code 139, cmd /opt/ros/hydro/lib/gazebo_ros/gzserver /home/a2ur4/catkin_ws/src/gazebo_ros_demos/rrbot_gazebo/worlds/rrbot.world __name:=gazebo __log:=/home/a2ur4/.ros/log/7e4dd822-cef3-11e3-85cd-001bb1f663f3/gazebo-1.log].
log file: /home/a2ur4/.ros/log/7e4dd822-cef3-11e3-85cd-001bb1f663f3/gazebo-1*.log
[gazebo_gui-2] process has finished cleanly
log file: /home/a2ur4/.ros/log/7e4dd822-cef3-11e3-85cd-001bb1f663f3/gazebo_gui-2*.log
all processes on machine have died, roslaunch will exit
shutting down processing monitor...
... shutting down processing monitor complete
done

How can I resolve? Thanks to all