Hi Terence,
FWIW...
I just restored my entire iPhoto library from Time Machine. I'm running Yosemite. After opening iPhoto for the first time after restoring the DB, it asked me to confirm my library location. Then it proceeded to update all the thumbnails. After this was completed, I observed what the OP reported: all photos work normally, but all videos were a.) missing thumbnails; and b.) yielding this error code when attempting to open.
HOWEVER. Doing a Reveal in Finder showed the videos on disk, and they were playable. After quitting iPhoto and restarting it, it *again* said it was updating thumbnails, and now all the videos both have the thumbnails and play correctly from within iPhoto.