Where did you download it from?
- If you bought it at the App Store, there is no serial number. If Aperture is asking for a serial number, someting is wrong.
- If you bought a serial number from the Apple Store (before the App Store was introduced) to unlock the Trial Version, you should have received an email with the serial number. Search your mail box.
If you cannot find a serial number, contact Apple for a replacement serial number.
See this link: Pro Application Replacement Serial Numbers
Do you have a second mac, where Aperture is still running? You can see the serial number in the "About" panel: In the Aperture menu in the main menu bar: Aperture > About Aperture.
This is me.
Are you sure, it is the AppStore version and not an Apple Store version? The version number suggests, you are running Snow Leopard and not Lion or Mt. Lion. With MacOS X 10.7.5 you should have been able to upgrade to Aperture 3.4.5 by now.
If you bought Aperture from the AppStore ( Not the pre-Lion Apple Store version), then the usual solution is to reinstall Aperture. Have you kept the installer you downloaded? You cannot download you current Aperture version again, since the AppStore version is now 3.4.5.
But if you downloaded Aperture from the Apple Store, you should have received a serial number by email. If you cannot find your serial number, contact Apple with a proof of purchase:
I'm running OS X 10.6.8
And yes my most recent version of Aperture is 3.2.4
I ( think) I bought it from the Apple Store, it was on sale, but like over a year and a half ago.
Looks like I do not have the installer and I cannot find the email confermation when I prchased it.
I know it's on the computer, at least the photos are, because I can access them in Iphoto and I can drag them out but Aperture still won't open.
Do you see Aperture in your "Purchased" list in the AppStore, when you sign in with your Apple ID?
What does it say? Installed?
If you see Aperture in your "Purchased" list,you could try to move it from the Applications folder to the Trash (don't empty the Trash), reload the "Purchased" tab with ⌘R, and download Aperture again, if you see the "Install" button.
If the AppStore does not offer a reinstall for version 3.2.4, I do not know how you could reinstall.