Aperture3: "internal" import function broken

Another one of those mysterious changes in Aperture's behavior when I have made no changes to settings.  Suddenly, the Import function of Aperture3 does not work.  (I can import files by drag-and-drop from Finder onto individual projects, but not from within Aperture using its menus and commands.)

Formerly, when I attached my card reader to the USB port, Aperture opened automatically, and I was presented with a screen of thumbnails of the files on the card, and was given the option of creating a new project or importing the files into an existing project.

Now, I must open Aperture manually, and when I attempt to import from the card reader, I get a blank window with a spinning ring and "Loading assets..." at the bottom.  Most menus are greyed out.  I have tried leaving the computer alone for as much as four hours, but when I return to it, the "Loading assets.." message is still there.

I have tried all three strategies in the Apple Support:  repairing permissions, repairing the database, and rebuilding the database.  No joy.   I have tried known good SD cards in the reader, and have tried other readers; they all behave the same.

Does anybody have suggestions what I should try next?