Edits in iPhoto create empty files
iPhoto '08 imports photos correctly, but creates empty files (0kb) once I edit. The original is retained correctly, and I can always "revert to original" to get the files back, but about a quarter of my edited photos show up as empty files when I try to view them. How can I fix it? Why does it happen to some, but not others?
Mac OS X (10.6.8)