OSC Preprocessing script fails

My directory folder is properly set up. I have 15 fit files in the lights folder, 15 flats in the flats directory ans 15 darks in the darks folder. preprocessing fails Wirth a message in the log saying no file was found for conversion. I’m running Siril 1.2.1 on a Mac mini (Mac OS Monterey) with an Intel i5 double core processor.
I’ve tried again and again. It always fails. Any tips and pointers? Thanks

hello, we need more info to help you, at least the log containing the directory names and the files layout, please see How to report issues — Siril 1.2.0 documentation

Do You have a bias folder?