Update to Aperture 3.2.2.
To recover missing images:
- Update to Aperture 3.2.2.
- After the update is complete, open Aperture and hold down the Command and Option keys until the Library First-Aid window appears.
- Choose the Repair Database option and click the Repair button.
When Aperture reopens after the repair has completed, the missing images will be visible again.
Note: These steps will recover the masters but not any versions or edits you may have created.