There is a problem with the CountPages plugin, and it looks like it's related with the jobs. It doesn't calculate the number of pages (Adobe method) and the calibre debug log is:
Spoiler:
-------------------------------
Logfile for book ID 14487 (Murder at the Marina)
Method of counting _page_count_mode=Estimate _download_sources=[]
results= {}
14487
do_statistics_for_book: C:\Users\moret\AppData\Local\Temp\calibre_trdzoz\0 ynht3_count_pages\14487.epub 2 Estimate [] [u'PageCount'] 1500 False
Traceback (most recent call last):
File "calibre_plugins.count_pages.jobs", line 155, in do_statistics_for_book
File "calibre_plugins.count_pages.statistics", line 53, in get_page_count
File "calibre_plugins.count_pages.statistics", line 92, in _open_epub_file
File "site-packages\calibre\ebooks\oeb\iterator\book.py", line 149, in __enter__
File "site-packages\calibre\ebooks\oeb\iterator\book.py", line 88, in run_extract_book
File "site-packages\calibre\utils\ipc\simple_worker.py", line 230, in fork_job
File "site-packages\calibre\utils\ipc\simple_worker.py", line 123, in communicate
WorkerError: Worker failed