"Sorry, an error has occured. The application could not be installed because the AIR file is damaged

Hello-

I have an air application that is distributed via CDROM, the app is signed by a code signing certificate and timestamped. In mid-August when my certicate expired my users started calling stating that they couldn't install our product due to the following error: "Sorry, an error has occured. The application could not be installed because the AIR file is damaged. Try obtaining a new AIR file from the application author." From my understanding a timestamped application is taken at a point in time when it's generated so why would it matter if the certificate was still valid? I have since replaced the certificate and will need to redistribute to my (thousands of) users however when I test it out using a future date and time the same error occurs. Any information to help resolve this would be grately appreciated.