According to the note at the bottom of this Adobe KnowledgeBase page, there is a bug in Flex Builder 3 when you create a new Air application, it fails to insert the correct Air version into the application descriptor file (<app name>-app.xml).
You will need to try changing the namespace to either
xmlns=“http://ns.adobe.com/air/application/1.0” or
xmlns=“http://ns.adobe.com/air/application/1.1” or
xmlns=“http://ns.adobe.com/air/application/1.5” depending on which version of the runtime you have installed on your system.
It was very frustrating for me as I received copies of the files we were using in the Adobe MAX ‘Air Boot Camp’ sessions, and none of them were working for me on my laptop – while they worked just fine in the lab.
This is because the files were set to the 1.1 namespace, and I only had Air 1.0 on my laptop. Editing the descriptor namespace to ‘1.0’ allowed me to run the files fine – but naturally I wanted to update to the latest version of Air, so now I can change them to the ‘1.5’ namespace.
http://www.adobe.com/go/kb403919
