Problem with transform

Hey,
I have created a hello.world file. The simple_mobile_manipulator is a pioneer2dx model attached with a hokuyo lidar. I have added the plugin in the hokuyo model to be able to see the lidar data.
When I roslaunch the launch file, this world opens correctly. When I see the data of the hokuyo lidar on rviz, there is a error: **For frame [hokuyo_link]: Fixed Frame [map] does not exist on rviz**
How to solve this issue? This is the hello.world file. model://ground_planemodel://sunmodel://simple_mobile_manipulator0 0 0 0 0 0model://pioneer2dx2 0 0 0 0 0