launch file error: cannot launch node of type [map_server/map_server]

edit

I created a launch file that contains:

<launch>
  <param name="/use_sim_time" value="true"/>
  <node pkg="map_server" type="map_server" name="map_server_node" args="/home/maysam/fuerte_workspace/sandbox/mit/map.yaml"/>
</launch>

But the output is:

ERROR: cannot launch node of type [map_server/map_server]: can't locate node [map_server] in package [map_server]

I can run the node manually and successfully:

rosrun map_server map_server /home/maysam/fuerte_workspace/sandbox/mit/map.yaml