If it only affects the Camera Roll then it's possible that the app is corrupted somehow. Offload the photos and then make a Genius Bar appointment with the nearest Apple Store if you don't want to take the time to restore the device and set it up as new.
Well the problems continue - hard reset fixes it, but then within a day later, it does it again until a hard reset. I guess we'll head to the genius bar unless someone else has an idea...