Problems adding .epub to calibre Mac OS High Sierra

All has been fine for about a month but now when I try to add .epub files to convert it gives me this error.
Any suggestions on what is wrong? Pdfs can be added with no issues.

calibre, version 3.14.0
WARNING: Errors while adding: There were problems adding some files, click "Show details" for more information
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Failed to add the file /Users/categibson/Documents/Ebook Files(Novels & Recipe Books)/Eaternity.epub to the book: /Users/categibson/Documents/Ebook Files(Novels & Recipe Books)/Eaternity
With error:
Traceback (most recent call last):
File "site-packages/calibre/gui2/add.py", line 430, in add_formats
File "site-packages/calibre/db/cache.py", line 1410, in add_format
File "site-packages/calibre/startup.py", line 122, in local_open
IOError: [Errno 21] Is a directory: u'/Users/categibson/Documents/Ebook Files(Novels & Recipe Books)/Eaternity.epub'