Do you use Windows Offline Files (also known as CSC) to sync your files between multiple computers? Are you using Redirected My Documents to sync your My Documents/Documents folder to all of your computers? Are you running Vista and having problems where either OneNote will crash or you get corruptions in OneNote? Is yes to these questions you are probably hitting a Windows Vista error with the offline files sync. In fact there is UI that appears in the Problem Reports and Solutions which tells you about this but until now there wasn't a fix available.
Last week when I saw this update that improves the performance and reliability of Windows Vista I saw this item in the list of fixes:
When you synchronize an offline file to a server, the offline file is corrupted.
I wondered to myself if this included the offline files problem we saw internally and lo and behold the fix is now public! If you have had problems with OneNote and Windows Offline files please download this fix: