Error advertising topic

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Hi there,

I am trying Gazebo 11 and few Worlds that ship with it. I am specifically looking at tracked_vehicle_simple.world

gzclient --verbose Gazebo multi-robot simulator, version 11.7.0 Copyright (C) 2012 Open Source Robotics Foundation. Released under the Apache 2 License. http://gazebosim.org

[Msg] Waiting for master. [Msg]

The world file loads correctly but then I get this error:

gzclient --verbose Gazebo multi-robot simulator, version 11.7.0 Copyright (C) 2012 Open Source Robotics Foundation. Released under the Apache 2 License. http://gazebosim.org

[Msg] Waiting for master. [Msg] Connected to gazebo master @ http://127.0.0.1:11345 [Msg] Publicized address: 192.168.1.76 Topic [/data://world/default/model/simple_tracked/plugin/keyboard_control/joint_cmd] is not valid. [Err] [JointControlWidget.cc:393] Error advertising topic [/data://world/default/model/simple_tracked/plugin/keyboard_control/joint_cmd] Topic [/data://world/default/model/simple_tracked/plugin/simple_tracked_vehicle/joint_cmd] is not valid. [Err] [JointControlWidget.cc:393] Error advertising topic [/data://world/default/model/simple_tracked/plugin/simple_tracked_vehicle/joint_cmd]

Any clue?

Thanks.