name 'namespace' is not defined + Invalid <param> tag

[johnwaneboy]

There is a strange issue. I have install and run the program successfully, and no adjustments were made. When I ran again, the following problems occurred. I reinstall and run, the same problem is the same.

name 'namespace' is not defined
when evaluating expression 'namespace'
when processing file: /home/wane/catkin_ws/src/rotors_simulator/rotors_description/urdf/component_snippets.xacro
included from: /home/wane/catkin_ws/src/rotors_simulator/rotors_description/urdf/hummingbird_base.xacro
included from: /home/wane/catkin_ws/src/rotors_simulator/rotors_description/urdf/mav_generic_odometry_sensor.gazebo
RLException: while processing /home/wane/catkin_ws/src/rpg_quadrotor_control/simulation/rpg_rotors_interface/launch/basics/base_quad_simulation.launch:
while processing /home/wane/catkin_ws/src/rotors_simulator/rotors_gazebo/launch/spawn_mav.launch:
Invalid tag: Cannot load command parameter [robot_description]: command [['/opt/ros/melodic/lib/xacro/xacro', '/home/wane/catkin_ws/src/rotors_simulator/rotors_description/urdf/mav_generic_odometry_sensor.gazebo', 'enable_logging:=false', 'enable_ground_truth:=true', 'enable_mavlink_interface:=false', 'log_file:=hummingbird', 'wait_to_record_bag:=false', 'mav_name:=hummingbird', 'namespace:=hummingbird']] returned with code [2].

Param xml is
The traceback for the exception was written to the log file

[CK1201]

ethz-asl/rotors_simulator#695