Hi Ric,
It's odd.
- Do you have a backup? Can you restore it to another location, or open it as is, and see if that older Library has the same problem?
- Confirm that you are in Browser mode and not Viewer mode.
- Confirm that no Images are selected ("Edit ▹ Deselect all")
- Confirm that the container you are viewing is, in fact, a Project. (Sorry, but more than a few users are confused by the parts of Aperture.)
- Confirm that there is NO filter set for the Project. Click the magnifying glass icon _in_ the search field in the Browser and select "Show all".
Nothing?
Reboot and check again.
Still nothing?
Repair your Library. Details are on Apple's Aperture trouble-shooting page. After repair, look for a Project called "Recovered" or something like that. As with every computer file, you should never use one without having a full back-up. This means, if you already have a back-up, to make a new, second back-up of your current Library before running the repair.
Still nothing? Post what you know. It's uncommon.
The next step is to rebuild your Library. I have _never_ had to rebuild a Library, though I have done it just to see how it works. It works well. Nonetheless, it is a last resort, and not one I think you'll need.