Hi, still no answer to this?
I have kind of the same problem, my Desktop preferences does not show more than a row named Aperture that is not expandable.
In other applications like Screensaver preferences, mail ... the Aperture library shows up and i can use pictures, projects, smart albums.
Any ideas for how to solve this? I have tried to move the library, change the name, regenerate the previews ... but nothing seems to work. I have populated iPhoto with pictures and it works just fine.
Edit: Just realized that if i create a new A3 library the problem is gone. Can there be any sizelimitations? My library contains 24000+ images and the size is aprox 100GB. It is also stored on a external harddrive if that can be a factor.