help please: invalid application descriptor

Hi,

When I run an mxml file, I'm getting the error:

                 invalid application descriptor: versionNumber must have a non-empty value

Can you tell me where "versionNumber" field is?  I cannot find it.   This is my -app.xml leading lines:

     <?

     <applicationxmlns="http://ns.adobe.com/air/application/2.5">

You see, I copied an example from someone running AIR 2, and I updated the number at the end from 2 to 2.5, which matches the code I'm doing, which works fine. 

But the example still doesn't run, and I can't find the versionNumber field, so ???

Thanks

---------------------------------------------------------------------  FULL ERROR BELOW -----------------------------------------------------------

Process terminated unexpectedly.

invalid application descriptor: versionNumber must have a non-empty value.

Launch command details:  "C:\Program Files\Adobe\Adobe Flash Builder Burrito\sdks\4.5.0\bin\adl.exe" -runtime "C:\Program Files\Adobe\Adobe Flash Builder Burrito\sdks\4.5.0\runtimes\air\win" "C:\Users\Reto\Adobe Flash Builder Burrito Preview\ExternalResources\bin-debug\ExternalResources1-app.xml" "C:\Users\Reto\Adobe Flash Builder Burrito Preview\ExternalResources\bin-debug"