[MapProxy] Installing virtual environment throws an OSError

[Jonas Saul]

Hi!

After installing C:\Python27\python path\to\virtualenv.py 
c:\mapproxy_venv it throws an error: "OSError: Command 
c:\mapproxy_venv\Scripts\python.exe -c 
"#!python\"\"\"Bootstra...sys.argv[1:])"
I'm out of ideas what causes the problem and how to fix it.
Running OS: Windows 7 Professional x64

Installation process and error:

C:\Python27>python C:\Python27\virtualenv.py c:\mapproxy_venv
New python executable in c:\mapproxy_venv\Scripts\python.exe
Installing setuptools.........
   Complete output from command c:\mapproxy_venv\Scripts\python.exe -c 
"#!python
\"\"\"Bootstra...sys.argv[1:])

" --always-copy -U setuptools:
   Searching for distribute
Reading http://pypi.python.org/simple/distribute/
Reading http://packages.python.org/distribute
Best match: distribute 0.6.36
Downloading 
http://pypi.python.org/packages/source/d/distribute/distribute-0.6.36.tar.gz#md5=a923385de72dcdca68cd4ac2b9dc1148
error: None
----------------------------------------
...Installing setuptools...done.
Traceback (most recent call last):
   File "C:\Python27\virtualenv.py", line 1965, in <module>
     main()
   File "C:\Python27\virtualenv.py", line 795, in main
     never_download=options.never_download)
   File "C:\Python27\virtualenv.py", line 895, in create_environment
     search_dirs=search_dirs, never_download=never_download)
   File "C:\Python27\virtualenv.py", line 588, in install_setuptools
     search_dirs=search_dirs, never_download=never_download)
   File "C:\Python27\virtualenv.py", line 562, in _install_req
     cwd=cwd)
   File "C:\Python27\virtualenv.py", line 863, in call_subprocess
     % (cmd_desc, proc.returncode))
OSError: Command c:\mapproxy_venv\Scripts\python.exe -c 
"#!python\"\"\"Bootstra...sys.argv[1:])

" --always-copy -U setuptools failed with error code 1

All the best,
Jonas