Loading failed in viewer

[db105]

I'm using the latest version (4.17). Books open very quickly in the editor, but in the viewer, they often take very long to open, and sometimes I get this error:

ERROR: Loading book failed
The details are:
calibre, version 4.17.0
ERROR: Loading book failed: Failed to open the book at C:\Users\Julio\Downloads\Calibre_library\Sarah Pinsker\A Song for a New Day (6848)\A Song for a New Day - Sarah Pinsker.mobi. Click "Show details" for more info.

Traceback (most recent call last):
File "site-packages\calibre\gui2\viewer\ui.py", line 444, in _load_ebook_worker
File "site-packages\calibre\gui2\viewer\convert_book.py", line 236, in prepare_book
File "site-packages\calibre\utils\lock.py", line 111, in __enter__
File "site-packages\calibre\utils\lock.py", line 91, in lock_file
File "site-packages\calibre\utils\lock.py", line 81, in retry_for_a_time
File "site-packages\calibre\utils\lock.py", line 66, in windows_open
WindowsError: [Error 32] The process cannot access the file because it is being used by another process.: u'C:\\Users\\Julio\\AppData\\Local\\calibre-cache\\ev2\\metadata.json'

Does anyone know what this is about? This has been happening to me since I migrated to versions 4.*

[kovidgoyal]

Something is locking the cached files the viewer uses. Typically antivirus/filesync programs. Try excluding the cache directory fro them.

[db105]

Originally Posted by kovidgoyal

Something is locking the cached files the viewer uses. Typically antivirus/filesync programs. Try excluding the cache directory fro them.

Thanks. I have excluded the cache directory from Windows Security and it seems to have worked. What a relief.