The update created a new Library
That is unusual. The update should have opened your previous Aperture library just fine. Is your previous Aperture library on an external volume? And is that volume not formatted for mac?
However, you should be able to import your previous Aperture library into your current Aperture library or vice versa.
See the manual page: Working with Library Files (the paragraph on Merging Libraries)
This doesn't work. I can export to the desktop as a "new" library, but Aperture is only "seeing" one Library even though when I switch using File>Library>Other it goes to the "old" Library, but then it doesn't see the "new" Library.
Put another way, both Libraries seem to be there, but only one can be seen one at a time.
I'm (slowly) exporting the "old" Library to the desktop, but I don't know if the "new" Library will accept it as folder or not.
Both are in "Pictures" on the HD, where they've always been, but only shows up at a time; whichever one I last used is the one I see/open. But it can't import one to another because it can't "see" both Libraries at the same time.
It might be that the process only works with two seprate computers, not wihin the same computer?
Sorry if that doesn't make much sense, but that's how it looks.