ApertureToZenfolio is an Apple Aperture export plug-in that uploads photos to Zenfolio. Download the latest version, unzip and run the installer. If you have previously installed manually to your user directory please remove the existing plugin. The installer will place the plugin in the shared /Library directory.
You can download it without the installer if you need to. Place it into your /Library/Application Support/Aperture/Plug-Ins/Export for all users or ~/Library/Application Support/Aperture/Plug-Ins/Export folder for just your user account. You will need to create the folder if it doesn't exist.
If you have any support issues please post in the Zenfolio forum.