Hi all, I am trying to use the navigation package, and I've exactly followed the tutorial from http://www.ros.org/wiki/navigation/Tutorials/RobotSetup But I was stuck in the move_base.launch file mentioned in the tutorial. Below is the error I got: load_parameters: unable to set parameters (last param was [/move_base/global_costmap/laser_scan_sensor/clearing=True]): cannot marshal None unless allow_none is enabled My move_base.launch is exactly the same as the tutorial: If i remove the last three lines, it worked through (It wont be functioning correctly of course). I deleted the three lines below: BTW, I have a simple question that how we set the starting location of the robot in the map? Thanks for your time. Chris -- View this message in context: http://ros-users.122217.n3.nabble.com/problem-about-move-base-in-navigation-stack-tp2096229p2096229.html Sent from the ROS-Users mailing list archive at Nabble.com.