It sounds like you are encountering an issue with your OneNote files where they are not accessible, indicated by the red X on the embedded files. This problem can occur for several reasons:
- Network Issues: Your OneNote Notebook content may not be synced completely with the SharePoint Online or OneDrive for Business server. Ensure that you have a stable internet connection.
- Account Authentication: Verify that you are signed in to your OneNote account. If your account is not authenticated, you may not be able to access your files.
- Offline Mode: Check if the OneNote client is set to offline mode, which would prevent access to synced content.
- File Location: If the files are stored in OneDrive for Business or SharePoint Online, ensure that they are not deleted or moved. You can follow the steps to restore your OneDrive content if necessary.
To troubleshoot, try the following steps:
- Check your internet connection and ensure you are online.
- Sign out and sign back into your OneNote account.
- Verify if the files are accessible from another device or through the OneDrive or SharePoint web interface.
- If the issue persists, consider moving the content to a new section if it is visible on another device.
If you continue to experience problems, you may want to consult the Microsoft Community for further assistance.