Most of the troubleshooting discussions say the only solution is to reintall the application but I can't find the Aperture DVD and the app store recognizes that I already have Aperture. An alternate solution would be appreciated. Thank you.
Before you reinstall, move the Aperture application to the Trash. Then the AppStore will not find it.
Use the Trial to reinstall, when you cannot find your cds.
See this knowledge base article by Apple:
After installing the trial it is important not to try to launch Aperture, but immediatly to upgrade using software update.
Once you are running Aperture 3.4 again, repair your Aperture library.
Added: I see, Aye Es Oh already answered this Good Luck!