Stange error- Spine is empty

[DragoLord19d]

calibre, version 7.8.0
ERROR: Loading book failed: Failed to open the book at C:\Users\Owner\Documents\MEGA\Calibre\AlgernonInWo nderland\Porter sur toi un nouveau regard (338)\metadata.opf. Click "Show details" for more info.

Failed to convert book: C:\Users\Owner\Documents\MEGA\Calibre\AlgernonInWo nderland\Porter sur toi un nouveau regard (338)\metadata.opf with error:
InputFormatPlugin: HTML Input running
on C:\Users\Owner\Documents\MEGA\Calibre\AlgernonInWo nderland\Porter sur toi un nouveau regard (338)\metadata.opf
Parsing all content...
Failed to run pipe worker with command: from calibre.srv.render_book import viewer_main; viewer_main()
Traceback (most recent call last):
File "runpy.py", line 198, in _run_module_as_main
File "runpy.py", line 88, in _run_code
File "site.py", line 95, in <module>
File "site.py", line 90, in main
File "site.py", line 50, in run_entry_point
File "calibre\utils\ipc\worker.py", line 196, in main
File "<string>", line 1, in <module>
File "calibre\srv\render_book.py", line 948, in viewer_main
File "calibre\srv\render_book.py", line 939, in render_for_viewer
File "calibre\srv\render_book.py", line 916, in render
File "calibre\ebooks\oeb\iterator\book.py", line 64, in extract_book
File "calibre\customize\conversion.py", line 245, in __call__
File "calibre\ebooks\conversion\plugins\html_input. py", line 113, in convert
File "calibre\ebooks\conversion\plumber.py", line 1336, in create_oebbook
File "calibre\ebooks\oeb\reader.py", line 97, in __call__
File "calibre\ebooks\oeb\reader.py", line 724, in _all_from_opf
File "calibre\ebooks\oeb\reader.py", line 369, in _spine_from_opf
calibre.ebooks.oeb.base.OEBError: Spine is empty

[jhowell]

From the log it appears that you are trying to open a metadata.opf file in your calibre library as if it was an actual book. It is not.