December 2022 - Unable to combine files for PDF

I created a pdf from jpg files on my computer last night with no trouble. This morning I needed ro do it again with the same files and kept getting a red error message saying 'The file is either password protected, encrypted or is a PDF form that could not be combined to generate the PDF file.'

I was able to get around it once by re-saving the component files from the same PSDs into JPGs with different filenames - which worked once, but then when I did it again one minute later I got the same error message and had to re-save to yet a different filename.

If anyone else has had this and knows what's going on I'd appreciate some help. Thank you.