не работает mkvirtualenv. ImportError: 'module' object has no attribute 'main'

при попытке создать новое виртуальное окружение на сервере Ubuntu возникает ошибка

~$ mkvirtualenv test
Traceback (most recent call last):
  File "/usr/local/bin/virtualenv", line 11, in <module>
    load_entry_point('virtualenv==1.7.1.2', 'console_scripts', 'virtualenv')()
  File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 489, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2852, in load_entry_point
    return ep.load()
  File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2443, in load
    return self.resolve()
  File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 2453, in resolve
    raise ImportError(str(exc))
ImportError: 'module' object has no attribute 'main'

virtualenv и virtualenvwrapper установлены

workon работает