I just checked the description for the 'Scene updater' tool on Maxon labs:
https://labs.maxon.net/?p=3258
- download link at the bottom of hat page if you want it.
"With Cinema 4D R20 the ability to load scenes, that got saved with Cinema 4D versions older than R12, has been removed.
The plugin described herein is supposed to help users locate such scenes and, when running in a version which still has the ability to load such scenes (e.g. R19), it can convert these to a newer file format, which can then be loaded in R20 again."