I followed the steps you gave me, BUT this caused Aperture 3 to completely crash, and rendered it unopenable. All I can say is NEVER hold down option and command while opening Aperture.
I did manage to fix things, and complete the update in this way:
1. Uninstalled Aperture 3
2. Reinstalled Aperture 2, and then installed aperture 3
3. Opened finder, and moved my Aperture Library to my destop
4. Successfully installed Aperture update 3.4.5 without a hitch
5. Moved my aperture library back into finder/pictures, replacing the empty one that was created during the Aperture installation
I hope this helps anyone else who had the same problem