How to locate unreferenced image in Aperture?

Question

I'm importing my Aperture library into an Aperture library on an external drive.

The issue is that I have some files which can't find their master (or reference? I'm still not sure of Aperture's verbiage). They all have the icon in the lower right corner:

But I'm not sure how to make that go away / connect it back to the original image. When I right click and go to "Locate Referenced Files" I can't navigate into the Aperture drive on my computer, where I know the file is.

How do I re-merge the library so those files are properly updated? Or just show it were the file is.

Answer 1

From an answer to How to tell Apple Aperture to store ALL files by reference?

For existing photos already in the monolithic library bundle, perhaps the "Relocate Original" command would be of assistance? You could move the original images to a new location, but keep the reference within Aperture.