Thanks Richard, Rob and Markus!

I cleared the entire directory and ran bootstrap.py again (Python 2.7.13) -- 

It's the same at the end:

===== Running in build: run configure.py

Traceback (most recent call last):

  File "bootstrap.py", line 2113, in <module>

    run()

  File "bootstrap.py", line 2108, in run

    enable_shared=options.enable_shared,

  File "bootstrap.py", line 1036, in run

    i.run()

  File "bootstrap.py", line 189, in run

    raise RuntimeError("Could not run %s: File not found" % executable)

RuntimeError: Could not run base\bin\python: File not found

Just to show that the '.exe' is not required on Windows:

C:\cctbx_17>c:\Python27\python

Python 2.7.13 (v2.7.13:a06454b1afa1, Dec 17 2016, 20:53:40) [MSC v.1500 64 bit (

AMD64)] on win32

Type "help", "copyright", "credits" or "license" for more information.

>>>

There is a python.exe in \base\bin\python, btw.

Horst