C:\envs\py2.6>pipenv --python 2.6
Creating a virtualenv for this project…
Pipfile: C:\envs\py2.6\Pipfile
Using C:/Python26/python.exe (2.6.6) to create virtualenv…
[  ==] Creating virtual environment...Running virtualenv with interpreter C:/Python26/python.exe

Failed creating virtual environment
[pipenv.exceptions.VirtualenvCreationException]:   File "d:\python_learn\lib\site-packages\pipenv\vendor\click\decorators.py", line 17, in new_func
[pipenv.exceptions.VirtualenvCreationException]:       return f(get_current_context(), *args, **kwargs)
[pipenv.exceptions.VirtualenvCreationException]:   File "d:\python_learn\lib\site-packages\pipenv\cli\command.py", line 208, in cli
[pipenv.exceptions.VirtualenvCreationException]:       clear=state.clear,
[pipenv.exceptions.VirtualenvCreationException]:   File "d:\python_learn\lib\site-packages\pipenv\core.py", line 574, in ensure_project
[pipenv.exceptions.VirtualenvCreationException]:       pypi_mirror=pypi_mirror,
[pipenv.exceptions.VirtualenvCreationException]:   File "d:\python_learn\lib\site-packages\pipenv\core.py", line 506, in ensure_virtualenv
[pipenv.exceptions.VirtualenvCreationException]:       python=python, site_packages=site_packages, pypi_mirror=pypi_mirror
[pipenv.exceptions.VirtualenvCreationException]:   File "d:\python_learn\lib\site-packages\pipenv\core.py", line 935, in do_create_virtualenv
[pipenv.exceptions.VirtualenvCreationException]:       extra=[crayons.blue("{0}".format(c.err)),]
[pipenv.exceptions.VirtualenvCreationException]: Traceback (most recent call last):
  File "d:\python_learn\lib\site-packages\virtualenv.py", line 51, in <module>
    print("ERROR: {}".format(sys.exc_info()[1]))
ValueError: zero length field name in format

Failed to create virtual environment.