Open the manipulator/open_manipulator/open_manipulator_control_gui and open launch/open_manipulator_control_gui.launch
Replace
<arg name="robot_name" default="open_manipulaotr"/>with
<arg name="robot_name" default=""/>save and move to workspace root and re build the workspace
cd roboticscatkin buildor
catkin_makeInstall following package if you get following error,
Error:
Could not load controller 'gripper_sub_position' because controller type 'effort_controllers/JointPositionController' does not exist.Package to be installed:
sudo apt-get install ros-melodic-effort-controllers