invalid application descriptor: Unknown namespace

I'm wanting to learn adobe air, so I can leverage my HTML/JavaScript skills in desktop development, but I've hit a snag just trying to get the sample HelloWorld app to run. I'm getting the following errer:

>adl HelloWorld-app.xml

invalid application descriptor: Unknown namespace: http://ns.adobe.com/air/appl

cation/2.7

As far as I've been able to tell, that is the correct namespace.

My Air runtime is 2.7.0.19480

My SDK is 2.7

Any help would be greatly appreciated.