iPhoto 11: Some files are unrecognizable

This has happened twice now: I try to import photos from a Nikon Coolpix camera to iPhoto 11 (OSX 10.8.4). Most are accepted but iPhoto complains that a few use an unrecognizable format. They are all jpegs.

After reading similar posts here, I have tried: creating a new library, rebuilding the library thru iPhoto and rebuilding the library thru iPhoto Library Manager.

The error message includes a file path that looks like this:

/Users/MyAccount/Pictures/iPhoto Library/Import/Masters/Roll 1/DSCN0999.JPG

Here's where I reach the limits of my education: When I look at the Package Contents of the iPhoto Library, there is no directory named Import. There is a Masters folder on the root level, but it does not contain a folder named Roll 1 and I can't find any sign of a file named DSCN0999.JPG.

Perhaps I should mention that these problems began after I transferred the iPhoto Library from a much older Mac (one of the old Motorola chip machines)... so old that I couldn't use Migration Assistant.