HI everyone, I'm making my final year project using Summit XL, but im having some problems with Gazebo launching. When I execute the command: roslaunch summitxlsimbringup summitxlcomplete.launch Then gazebo and rviz open, but there's no world and the robot seems to sink slowly and this errors appear in the command window: Error [parser.cc:581] Unable to find uri[model://sun] Error [parser.cc:581] Unable to find uri[model://groundplane] Error [parser.cc:581] Unable to find uri[model://willowgarage] How could i fix it? :)