I’ve been experiencing this error while working on a air project using an ANE extension. After a while, I found that the descriptor namespace of my extension was set to a later version of my Air SDK which was Flash Pro CS6’s default Air SDK 3.4.
In the extension file (located for me, on my mac in user/you/Library/Caches/TemporaryItems/Tmp_ANE_File_Unzipped_Packages/idOfYourExtension/META-INF/ANE/extension.xml) simply change the extension descriptor (first line) to your SDK version :
You can find here help on extension descriptor namespace
Exemple of extension descriptor file