There are many reasons for that, please follow the checklist below.
- Check if you have only Core folder in /wp-content/themes. If you have something like ex. /wp-content/themes/Core-v2-5/Core then please upload only Core folder to /wp-content/themes
- Check if file path /wp-content/themes/Core/js/jquery.ppflip.js is not forbidden on your server.
- Check if you setup homepage gallery via Core admin > Homepage > Choose Homepage Gallery