This is one of the easiest fixes ever, but I believe I’m the first on the internet to blog about this issue. The issue arises when building a mobile project in Adobe Flash Builder with the Air namespace. In the *-app.xml file, the namespace is what is used to define whether the XML document is “well-formed” or not.
If your [project]-app.xml file is generating a namespace error, it could be one of two things. The first is simply that the namespace version is not up-to-date. In this case, the “problems” panel will show you which version you should be using.
If it’s saying your version is 0.0.0 and you know you have 3.1 or 3.2 in the namespace, then you probably have the same issue. Here’s the error message:
namespace 0.0 in the application descriptor file should be equal or higher than the minimum version 3.1 required by flex sdk
If this issue comes up, your problem might be as simple as directional quotes. This could happen if you have typed ‟ or ” rather than “. The solution is simple. Make sure that your quotation marks are not directional. Here’s how your namespace declaration should look.
Hope that was helpful for you.