Every hard drive has a volume name (they also have a UUID but I don't think Aperture cares about that.) If the new drive was not given the same name as your old drive then as far as Aperture is concerned, the drive it's looking for is not present (it's looking for a drive with a specific name and not finding it.)
While YOU know that all the data on the old hard drive was copied to the new hard drive, Aperture doesn't know that (and makes no assumptions). So if the volume name it's looking for isn't found, then the drive is "offline". Aperture is working as it should.
You could rename the hard drive back to the original name, but then that would just cause it lose all any new 'referenced' masters you added since upgrading the drive.
You'll need to reconnect the masters. In the lower right corner of the thumbnail you should see a small icon which ordinarily has a tiny rectangle with an arrow pointing away (indicating this image is a "referenced" master). If the master is missing you'll have a little orange triangle with the "!" inside it (indicating a problem).
In the main menu, select "File" -> "Locate Referenced Files..."
A box will appear and you can check the box which reads "Show Only Files Not Found" (this will hide all the files which are currently fine so that you only have to deal with the files that have a problem.)
In the lower part of the panel is filesystem browser. You can navigate to the directory drive & directory where these files are located and click "Reconnect" or, if they're all in the same place, "Reconnect All".
Pick "Done" when you've finished.
If you don't like using "referenced" masters, you can tell Aperture to bring the masters into the Aperture Library so that it will manage the files for you (and avoid this problem in the future). In the main menu pick "File" -> "Consolidate Masters". You'll be given the choice to "copy" the files (it'll copy the masters but still leave the old files back in their original locations... but Aperture will no longer need those originals.) or you can "move" the files (Aperture will copy them into the library then delete the original after the copy is completed... effectively "migrating" the masters into your library and cleaning up the originals when it's done.
Last night I connected my iPhone with Personal Hotspot on, (I forgot to turn it off before doing so) causing my Mac Pro to kernel panic. The problem is, I was in the middle of an Aperture operation relocating masters from a project and making them referenced on a second drive.
My problem is for the photos affected in the middle of the panic, is that I have the yellow triangle but I when I click on Locate Referenced file, I get an error saying that "The selection does not have any referenced files' despite the shortcut icon.
If I click the image to its left and the problematic image, I get the file reference dialog box, and the raw image does show on the second new drive, yet Aperture refuses to reconnect it. Its as if it doesnt see the connection. How can I force an image to reconnect to its Master when Aperture refuses to ackowledge that that is exactly what we are trying to achieve. I basically have 25 photos from the project that have matching NEFs that I just cant reconnnect. Any ideas?