That icon indicates Aperture has lost the link to a referenced original. If the original file still exists, the fix is to point Aperture back to it using Locate Referenced Files. If the file is not in a normal accessible folder but still inside an Aperture library bundle, a useful command is Relocate Original. That moves existing originals out to a chosen folder location while keeping them referenced by Aperture.

So, if these images are currently managed inside the library package, use Relocate Original first to place them in a regular folder on your drive. Once the originals are in an accessible location, Aperture can maintain the reference properly. If they’re already external, use Locate Referenced Files to reconnect them to their current folder.

In short: missing icon = broken reference; Relocate Original helps when the originals are still buried in the library bundle; Locate Referenced Files is for reconnecting to accessible originals.