Error while installing using pip

[german-bortoli]

I am using ckan version 2.6.0 under ubuntu 14.04

If I execute pip install ckanext-s3filestore it exit with this error.

I did the previous steps which was enable virtualenv

  File "/usr/lib/ckan/default/lib/python2.7/site.py", line 703, in <module>
    main()
  File "/usr/lib/ckan/default/lib/python2.7/site.py", line 683, in main
    paths_in_sys = addsitepackages(paths_in_sys)
  File "/usr/lib/ckan/default/lib/python2.7/site.py", line 282, in addsitepackages
    addsitedir(sitedir, known_paths)
  File "/usr/lib/ckan/default/lib/python2.7/site.py", line 204, in addsitedir
    addpackage(sitedir, name, known_paths)
  File "/usr/lib/ckan/default/lib/python2.7/site.py", line 173, in addpackage
    exec(line)
  File "<string>", line 1, in <module>
KeyError: 'ckanext'