I am developing in the standalone Flex Builder 3 Standard IDE, running the latest Flash Player and matching debug player 10.0.32.18 and have installed the new AIR 1.5.2 runtime.
I have an AIR application that is built on the Flex 3.2 SDK. When I change the app.xml descriptor to namespace to <application xmlns="http://ns.adobe.com/air/application/1.5.2"> and try to debug the app, I get the "invalid application descriptor ......" error. Also, if I simply try to run the app (not debug it), it won't launch. In fact Flex Builder just sits there.
What am I missing? If I set the namespace back to <application xmlns="http://ns.adobe.com/air/application/1.5">, everything works again.
You need to update the AIR SDK to 1.5.2.
If you are on Mac, you can mount the SDK dmg file, then ditto it over the flex sdk dir insider your Flex Builder.