The following checklist can be useful to tackle possible causes of the problem.
This message appears on running BornAgain.exe if BornAgain cannot find Python libraries.
If Python is correctly installed on the system according to Install Python environment, check if it discoverable by the system. Open command line or PowerShell and type
$ python
If Python interpreter has not started, then its installation directory is not in system PATH.
Open
Edit the system environment variables -> Environment variables -> System variables -> Path -> Edit
and add Python installation directory to the end
Having more than one Python interpreter installed on the system may cause subtle errors. Managing their co-existence is possible, but may require special skills. It may be preferable to uninstall all Python versions but one.
BornAgain is a 64-bit application and requires a 64-bit Python3 installed on the system.
The Python version number, indicated in the BornAgain installer name
(e.g. BornAgain-20.2-python3.9-win64.exe) must
match the Python installation on your system.