I encountered this same error while backing up my iPhoto library. I was able to find the exact file causing the error by creating a sparse disk image then dragging the library folder into the image. It was an iterative process as the file copy failed and it reported the name of the problematic file, then I'd find and delete the file, then start over, create a new disk image, copy the folder again, get the name of the next file causing the problem, delete it and start again. Finally the copy successfully completed. I think I caused the two file corruption issues by force quitting iPhoto when it appeared to hang a while back.
Note that in both cases the files were not found in iPhoto. I did a unix find to locate the corrupted files deep in the iPhoto library folder.
Cheers.