Thank you, Walt!
Dumping Sony Reader was my plan from the outset
But there is no success yet.
1. Uninstall Sony Reader, then uninstall calibre, restart, re-install calibre --> same Python error message
2. Uninstall calibre again, do full anti-malware run, defrag disk, re-install calibre --> same Python error message
3. uninstall calibre, check disk with ScanDisk, re-install calibre --> same Python error message
4. uninstall calibre, uninstall the program owning the snippets seeping through in the Python error message, restart computer, re-install calibre --> same Python error message
5. uninstall calibre, run regedit, removing alle remaining references to Sony Reader, calibre and python, re-install calibre but still no luck.
Came to my mind: Recently Windows wanted to check C:\ at start-up. I saw no reason not to and let it run ScanDisk. There were some messages about index.dat being repaired, but the messages quickly disappeared and I haven't seen the full story. This probably was the session when calibre failed the first time, though I'm not sure.
Anything else before re-installing Windows?
Roel