Unknown Issue On Onenote

[LouBazalgette]

I have the document in OneNote 2010, but there is a problem, I can't open it cause of - OneNote may need to repair the file in order to read it. This message has appeared today at opening it. Yesterday the document was valid.

[Buenchico]

Moderator's note:
Posts here from new members about corrupt files have a nasty habit of being followed by other posts from new members, with 'helpful' links to 'magic' software. i.e. they're poorly disguised spam. If such a link appears here I'll simply delete this thread.

However if this is a genuine post then
(a) welcome to AB ; and
(b) take a look here:
https://support.microsoft.com/en-us/help/825779/how-to-recover-information-in-a-damaged-onenote-section-file
(Although that page refers to earlier versions of OneNote, it should also be valid with your version)