To resolve this issue, reinstall Aperture 3.1:
- Click the Apple () menu in the upper-left corner of the screen and choose Software Update.
- After Software Update scans for updates, click the Show Details button. If any Mac OS X updates are available, install them. (If you are using Snow Leopard, your computer must be Mac OS X v10.6.4 or later to use Aperture 3.1).
- Download the Aperture 3.1 manual update.
- Follow the on-screen instructions to complete the Aperture installation.