Blank key photo in iPhoto & problems with other programs

I have iPhoto 8.1.2 with OS 10.7.2

I have not had any problems in the past, however I now have an annoying problem in iPhoto.

In my Events library I have 6 events that are now showing blank key photos (no picture is shown for them). The photos are in the events and are fine, however no key photo is shown. If I open the event and double-click a photo to assign it as a key photo it does not work.

The problem I have is that with, for example, Pixelmator I want to edit a photo. When I try to open a photo I have to select an event, however if I want to use a photo in a "blank" event Pixelmator won't let me open it. It does not see the photos in the event. If I click Open in the File Open window I just get an error the number of times there are photos in the event.

I have not done anything with the photos in the events and I don't know why it started doing this. I don't use iPhoto too often so I can't even tell you what I was doing when this happened.

Appreciate any help as I actually wanted to edit some of the photos in Pixelmator from the blank events.

First thing to try:

Open iPhoto with the option and command keys held down. In the resulting dialog box, check every option. Then go away and make some tea or something while it does it thing. For good measure (not really necessary but can't hurt), restart the machine. Now open iPhoto the normal way and see if that fixes the issue.

Before I do that, maybe I can just delete the event and reinstall the photos from my backup on my NAS. I purposely always download the photos from the camera to a folder on the NAS, and then import them to iPhoto from there (rather than importing them from camera to iPhoto right away).

That did not work. The 5 blank events are now gone.