file [rospack find turtlebot_navigation/nav_rviz.vcg] does not exist

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The error:

"File [rospack find turtlebot_navigation/nav_rviz.vcg] does not exist"

means that it could not find the vcg file in the turtlebot_navigation folder. It does not mean it could not load your map. All the vcg file does it help you configure your rviz environment. The file should be located in the turtlebot_navigation package. If not, try updating your software.

The error:

"Global Status Error: Target Frame - For frame [/kinect_rgb_frame]: Frame [/kinect_rgb_frame] does not exist"

means that the frame you are trying to view does not exist. Most likely your fixed frame in rviz is set to kinect_rgb_frame, to get rid of this error click on the fixed frame box and select a different frame from the list like base link. For an overview of how rviz works see here: http://www.ros.org/wiki/rviz/UserGuide.

Most likely the reason your map is not being displayed is because the map display module is not loaded. If you click on the add button at the right bottom of the rviz window, then select map and select ok. Once you have added the map module you must select the topic to listen to for the map, click on the topic field and select the map topic and the map should appear.

On a side note, you need to use more than roscore to bring up TurtleBot. sudo service turtlebot start actually just launches minimal.launch in turtlebot_bringup.