After import into iPhoto, originals disappear and only thumbnails remain

Question

After importing photos into iPhoto, working on them and then closing iPhoto, when reopening iPhoto only the thumbnails remain and can't find the originals anywhere on the computer via a Spotlight. Ran Disk Utility and no problems found on HD. Have rebuilt the iPhoto Library. This has happened on multiple occasions.

Answer 1

Here's a little more background on this problem. JPGs originally were imported from a CD and had camera given filenames, like 20110428-DSC_0118.jpg. After the import into iPhoto the application was closed. The next day when iPhoto was opened and any of the just imported photos doubled click on, a dialog box similar to this appeared that changed with the different file names:
I did a little research and discovered that the camera that had given filenames were identical to those by a different group of photos from a different camera that already resided in the iPhoto Library! So I imported them again from the CD except this time I used the utility, Better Finder Renamer 8, to batch change the names to something completely different, like Mary_Spring_2011_Visit_001.jpg, and so on. Those were imported into iPhoto. iPhoto was closed and opened and everything was OK. The next day iPhoto was opened and the newly imported photos when double clicked, the same exact dialog box as above opened and the only newly named photos that could be found were the thumbnails. None of the original full-res images can be found doing a Spotlight search of the entire computer. So to answer your second question the same dialog box shows up. I'm confounded as to where they are going. Plus, why would the original filename that was changed be showing up in the dialog box?? That is why Disk Utility was run to see if there was any directory damage. But no problems were found.