To fix OneNote not allowing you to insert a file or attachment into a locked notebook, please follow these steps:
- Verify you have write access to the location where you are trying to save the notebook
- If you are attempting to insert a file or image into a section, make sure you are on the same page where you want to insert the file
- Check tab permission and section permission for the notebook you are using
- If the issue persists, close down the notebook and restart the OneNote Application
- Make sure you have the most recent version of OneNote installed by checking for updates