How to troubleshoot photo import failure with Shotwell?

I can't get Shotwell to import my photos. They are all normal JPEG files from digital cameras, about ten thousand in total. How to I continue troubleshooting this, and get all my photos back into Shotwell?

I exported them from within Shotwell to a backup drive, prior to reinstalling Ubuntu 11.04. The export settings were: current format, original size, and export metadata selected. After exporting, I verified the files were all present, batch renamed them all with pyRename, and then opened a few at random to test. Now I've reinstalled and it's time to put them all back. I am having no luck at all. The only clue I have is the following error message in the ~/.cache/shotwell log:

[WRN] No namespace info available for XMP prefix `lr'

I can open the files now after the reinstall, with Eye of Gnome. I can even import them into F-Spot, complete with tags and full EXIF data. Everything seems normal about the files, except they won't import into Shotwell.

I tried the default version of Shotwell, then the Yorba ppa (0.11.1 version), neither will import. They chug away, I hear the hard drive activity for a while, then I get a 'No photos or videos imported' message.

If this is the wrong place for this question can anyone suggest a better place to post it? Yorba's wiki & list of bugs did not give me any meaningful search results.

I've got a second backup of the images prior to all this, but they are untagged and unsorted. Did I just waste a week tagging and sorting all my photos for nothing?