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Since I installed PTV Visum 18, Python does not work anymore in PTV Visum 17 (and older), *.py scripts cannot be referenced in the procedure sequence or any AddIn or Python scripts started over COM crash with an error message:
- 'Communication with the Python background script failed'.
- 'Could not start the script component'.
- 'Could not find a matching script component for file extension '.py'.'
- 'pythoncom error: ERROR: server.policy could not create an instance.'

Older versions of PTV Visum (17 and older) were shipped with Python 2.7.03. From PTV Visum 18 Python 2.7.15 is delivered. However, there cannot be multiple parallel installations of Python 2.7 on one system. To ensure a smooth handling of the previous versions (PTV Visum 15/16/17) with Python, install the following update:
- 15.00-24 for PTV Visum 15.
- 16.01-17 or higher for Visum 16.
- 17.01-10 or higher for PTV Visum 17.

If you are using even older versions than PTV Visum 15 (<= 14), you need to manually copy the following DLL files from the
.. \Windows\System32\
folder to the
.. \Program Files\PTV Vision\PTV Visum 14\Exe\
- python27.dll
- pythoncom27.dll
- pythoncomloader27.dll
- pywintypes27.dll