Since nobody here responded, I posted the issue in the PsychoPy github repository. Somebody came up with the answer. It seems there’s a DLL file installed on some Windows systems (but not all) called ‘libmmd.ddll’ (under the ‘C:\Windows’ directory) that was causing the problem. I just removed it (after saving a copy somewhere) and now PsychoPy is working. If you’re having a similar problem, you might try that. For more info, see https://github.com/psychopy/psychopy/issues/2267
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