What Happened to My Images?!
One problem we've seen reported from folks involves images in your notebook suddenly being replacd with "white pages" or "white boxes" with a red X in them. Unfortunately that's usually not a good thing.
One of the most common causes of this occurs when you convert a OneNote 2010 formatted notebook to OneNote 2007 format. The image formats in the new versions are different and OneNote sometimes has difficulty converting them.
Likewise the issue can sometimes be caused by antispyware or antivirus software interfering with the image creation process.
I don't have a good solution on how to recover from it, in fact as nearly as I can tell the damage is irreversible. Your best bet is to restore the previously-working notebook from backup.
One lesson learned here...be very careful about converting heavy image-laden notebooks from 2010 to 2007 format. In fact, I'd make a copy first of any notebook you intend to convert, then do the conversion and confirm that it looks o.k. before you delete the copy.