To recover a corrupt section, first try syncing your notebook manually. If that doesn’t work, then we recommend copying the pages from the corrupt section into a new section.
Click your notebook to see a list of all notebooks.
Hover over the notebook that shows the sign and in the error message note the name of the section that isn’t syncing.
Copy the pages from this section to a new section and then delete the damaged section.
Try syncing your notebook again.
Another alternative is to use OneNote 2013. If you have access to a PC and OneNote 2013 installed in it, open your notebook with the damaged section and the app will automatically attempt to repair your section. If you don’t have OneNote 2013, you can download and use the trial version of Office 2013 and Office 365.
Note: The OneNote touch app does not support repairing damaged sections.