roslaunch error

edit

I am trying to write a launch file which runs the nodes that are crated on a remote system named "turtlebot2" from my host computer "prasanna". When I run i get this error

This is my launch file:

<launch>
  <machine name="turtlebot2" address="10.0.10.28" ros-root="/opt/ros/electric/ros" ros-package-path="/opt/ros/electric/stacks" default="true" user="turtlebot2" password="turtlebot" >
  </machine>
  <node name="openni_tracker" pkg="openni_tracker" type="openni_tracker" respawn="true" output="screen" cwd="node" machine="turtlebot2"/>
</launch>

ERROR:

**prasanna@prasanna:~$ roslaunch launch launch_test.launch
... logging to /home/prasanna/.ros/log/705ad25e-888e-11e1-ac56-485d60f5f00e/roslaunch-prasanna-7286.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.
ERROR: unknown machine [turtlebot2]
prasanna@prasanna:~$ roslaunch launch launch_test.launch
... logging to /home/prasanna/.ros/log/705ad25e-888e-11e1-ac56-485d60f5f00e/roslaunch-prasanna-7292.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.
started roslaunch server http://10.0.10.30:47129/
remote[10.0.10.28-0] starting roslaunch
remote[10.0.10.28-0]: creating ssh connection to 10.0.10.28:22, user[turtlebot2]
remote[10.0.10.28-0]: ssh connection created
SUMMARY
PARAMETERS
 * /rosversion
 * /rosdistro
MACHINES
 * turtlebot2
NODES
  /
    openni_tracker (openni_tracker/openni_tracker)
ROS_MASTER_URI=http://10.0.10.28:11311
core service [/rosout] found
error launching on [10.0.10.28-0, uri http://turtlebot2-laptop:56525/]: Name or service not known
Launch of the following nodes most likely failed: openni_tracker/openni_tracker**

"launch" is the name of the package in my host computer and I want to run openni_tracker node on the turtlebot2. If there is a mistake in the launch file please help me out!