Just wanted to pass this on if anyone else runs into it...
After upgrading from CS5 to CS5.5, I ran my flash program for AIR 2.6 as normal, but the ADL (Air Debug Launcher) never opened.
(CS5.5 automatically changed the publish setting from AIR2.5 to 2.6)
It turns out the app-xml format had changed, and the ADL wouldn't open the air app due to an unrecognized format (I assume this was the problem).
Specifically, I changed
... and it started working!
You may also have to change
At the top so '2.6' reflects the version of AIR you are targeting. In my case I had to change 2.5 to 2.6
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