Ensure all downloads came from a trusted source:

1. Check the file extension to ensure it is compatible with OneNote.
2. Disable any security programs that are running on your system that is blocking the file.
3. Restart the system and try opening the file again.
4. If the issue persists try disabling OneDrive for Business – this can be done through the Settings> Accounts Panel.
5. Make sure you have all the latest Windows updates installed on your system.
6. Temporarily disable third-party anti-virus protection programs.
7. Make sure the file isn’t stored on a restricted source, such as a USB drive or external hard drive.