I just ran into a somewhat frustrating to debug problem with running the final release of Flex builder. I just upgraded to the final release version of Flex Builder 3 from a beta version, and I found that suddenly my AIR projects would no longer run from the IDE. When I clicked the "Run As Adobe AIR Application" button - nothing happened. No error, no nothing, it just doesn't seem to do a thing. Then I tried running the running the app in debug mode and got this error:

Process terminated without establishing connection to debugger.

Command:

"C:\Program Files\Adobe\Flex Builder 3 Plug-in\sdks\3.0.0\bin\adl.exe"
C:\wwwroot\MyApp\bin-debug\MyApp-app.xml 
C:\wwwroot\MyApp\bin-debug 

Output from command:

invalid application descriptor: descriptor version does not match runtime version

After a little Googling around and hitting a few dead ends, I finally found the simple solution on this post on Brian Rinaldi's Blog. For any AIR apps you created in earlier versions of Flex builder, you're going to want to take a look sat the application's xml descriptor and make sure it matches the version of the AIR runtime you are developing for. Just open up the descriptor XML file and make sure that the namespace specified is "http://ns.adobe.com/air/application/1.0", not "http://ns.adobe.com/air/application/1.0.M6", which was the last beta version.