Jarek: I can't easily test this in my environment; perhaps you can help. Could you change, in the file

c:\python27\lib\site-packages\pip\_vendor\distlib\resources.py,

line 40 from

            base = os.path.join(get_cache_base(), 'resource-cache')
to
            base = os.path.join(get_cache_base(), str('resource-cache'))

to see if that resolves the problem? Currently, 'resource-cache' is a Unicode string (because of "from __future__ import unicode_literals" in the containing module) and that causes Python to try and convert the get_cache_base() result to Unicode using ASCII, which leads to the failure.