[FRedlich]

Originally Posted by kovidgoyal

See https://manual.calibre-ebook.com/faq...e-is-not-valid

Yes you can delete them. It will degrade the reading experience a little, you may not get popup footnotes in some epub viewers as aresult.

This helped and I could upload the fixed epub file without any problems.
I see you are very active in supporting others. THANK YOU.