diamondback launch problem

edit

Greetings, I am facing some problem with diamondback setup. I am not able to execute common tasks like launching a node with roslaunch. Following is an example of such problem:

/opt/ros/diamondback/stacks/navigation_experimental/sbpl_lattice_planner/launch$ roslaunch  ./move_base_sbpl_fake_localization_2.5cm.launch 
    Traceback (most recent call last):
      File "/opt/ros/diamondback/ros/bin/roslaunch", line 2, in <module>
        from ros import roslaunch
    ImportError: No module named ros

Earlier i faced no such difficulty. Any idea what could be the reason ??? Does it amounts to reinstallation?

Update1: Environment variables

 $ echo $ROS_ROOT
    /opt/ros/diamondback/ros
    $ echo $ROS_PACKAGE_PATH 
    /opt/ros/diamondback/stacks
    $ echo $PYTHONPATH 
 /opt/ros/diamondback/ros/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/opt/ros/diamondback/ros/core/roslib

rxgraph problem: may be related.

/opt/ros/diamondback/ros$ rxgraph
Traceback (most recent call last):
  File "/opt/ros/diamondback/ros/bin/rxgraph", line 34, in <module>
    import roslib; roslib.load_manifest('rxgraph')
ImportError: No module named roslib

I updated ROS_PACKAGE_PATH

/opt/ros/diamondback/ros/core/roslib$ echo $ROS_PACKAGE_PATH 
/opt/ros/diamondback/ros:/opt/ros/diamondback/stacks

but error persists. thanks