The problem is, I think, that the environment of your Python installed in C:\Python27 becomes mixed with ATK, which is its own, independent Python interpreter and which should not and need not "see" any other Python on the system. If I'm not mistaken the root cause is the environment variable PYTHONHOME (and possible PYTHONPATH); on Linux we explicitly unset these when ATK is started, but not on Windows.
So, check your environment in the Control Panel and remove these variable. Or, you can create a BAT file launcher for VNL with the following contents
@echo off
set PYTONHPATH=
set PYTHONHOME=
cd <your home directory or whereever you want VNL to start>
vnl