Hi there! I understand you’re having trouble opening a book in the Crossword Jam app on your Mac with OS X 10.15. To get this sorted out, could you tell me a bit more? For example:

- Does the app itself open but the specific book won’t load, or does the whole Crossword Jam app fail to open?
- Are you connected to the internet when trying to open the book?
- Have you tried restarting the app or your Mac already?

This info will help me guide you better.

In the meantime, here are some general troubleshooting steps for Crossword Jam book loading issues:

1. Check your internet connection
Make sure your Mac is connected to a stable Wi-Fi or Ethernet network because the app needs to fetch the book data online.

2. Restart the app
Quit Crossword Jam completely and reopen it. On Mac, you can right-click the app icon in the Dock and choose “Quit,” then launch it again.

3. Restart your Mac
Sometimes a simple reboot clears temporary glitches.

4. Clear app cache or data if possible
While this is more straightforward on mobile, some Mac apps store data in specific folders. You can try deleting cache files related to Crossword Jam, often found in ~/Library/Caches/ or ~/Library/Application Support/. If you’re comfortable doing this, I can guide you.

5. Update the app
Ensure Crossword Jam is updated to the latest version through the Mac App Store.

6. Reinstall the app
If none of the above works, uninstall Crossword Jam and reinstall it fresh. This can fix corrupted files preventing books from opening.

If after trying these you’re still stuck, I’m here to dig deeper. Just let me know what steps you’ve tried already!

Are you satisfied with this initial guidance?