An error of "ERROR PYTHONPATH"

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Hi,

I want to make my ROS system clean by not having this one error. The error as I pasted below after invoking the command "roswtf". How should I go about this?

Output:

Loaded plugin tf.tfwtf
No package or stack in context
================================================================================
Static checks summary:

Found 1 error(s).

ERROR PYTHONPATH [/opt/ros/diamondback/ros/core/roslib/src:/opt/ros/unstable/ros/core/roslib/src:/opt/ros/diamondback/ros/core/roslib/src:] 
is invalid: Multiple roslib directories in PYTHONPATH (there should only be one)
================================================================================

ROS Master does not appear to be running.
Online graph checks will not be run.
ROS_MASTER_URI is [http://localhost:11311]

Thanks in advance..