App Installer file broken in AIR 20 and now also back in AIR 19

[yachts9999]

Mac OSX 10.11.2 Flash Pro CC 2015

After upgrading to AIR 20 and AIR 20 SDK, my AIR for Desktop app will create an installer file but that file will not run and fails with the error "The application could not be installed because the installer file is damaged".  I've reverted to version 19 (runtime and SDK) with the same results. The output from the Console app shows:

18/12/2015 10:01:02.631 Adobe AIR Application Installer[1437]: Got an unexpected fatal error while unpackaging: [ErrorEvent type="error" bubbles=false cancelable=false eventPhase=2 text="Missing necessary file META-INF/AIR/application.xml" errorID=0]

Any suggestions how to get this to install?

[yachts9999]

UPDATE:

I have now discovered that by altering the AppID slightly (changing one character), the application will now install.

Is there an old file that is causing the issue and so needs deleting?

[yachts9999]

Fixed this in the end but not sure why!

Ended up running the excellent Onxy maintemance/repair software from Titanium Software (http://www.titanium.free.fr/onyx.html) and now the installer works and the application installs inder AIR 20.