rosinstall error

edit

why when i try to run rosinstall i get this error:

Traceback (most recent call last):
  File "/usr/local/bin/rosinstall", line 5, in <module>
    pkg_resources.run_script('rosinstall==0.5.30', 'rosinstall')
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 467, in run_script
    self.require(requires)[0].run_script(script_name, ns)
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 1200, in run_script
    execfile(script_filename, namespace, namespace)
  File "/usr/local/lib/python2.7/dist-packages/rosinstall-0.5.30-py2.7.egg/EGG-INFO/scripts/rosinstall", line 28, in <module>
    import rosinstall.helpers
ImportError: No module named rosinstall.helpers