Slideshow feature suddenly failed on iPhoto 8.1.2

Clicking the slideshow arrow generates a gray screen, a brief flash, and a return to the Library window. This affects all my Libraries, including those on external drives. My failed attempts to fix include:

1. Removing iPhoto pref files.
2. Removing all iPhoto files from the Library folder.
3. Restarting.
4. Switching to a different user.
5. Reinstalling iPhoto.

This appears to be a problem with either a resource iPhoto needs for slideshows, an interfering file, or perhaps a permissions problem (something that has plagued me for years). Of course, the Great Gremlin God could have taken a dislike to me.

Any ideas? I really don't want to reinstall the OS to fix this.