Definition spark.effects:AnimateFilter could not be found.

You  are using the old sdk version. Spark supports available from sdk 4. Please add/update your sdk from Project Properties menu in Flash Builder

Access of undefined property JSON

First we have to download the library and can find it at http://code.google.com/p/as3corelib/. Then follow these steps to add your JSON library to your Flex project:

   1. Download the .zip archive and extract it. What you need is the .swc file in the lib folder.
   2. In Flex Builder / Flash Builder, go to your project’s properties, and then to the Flex Build Path panel.
   3. Click on Add SWC, and select the as3corelib.swc file
   4. In your project, add the following line: import com.adobe.serialization.json.JSON;

Error:Process terminated without establishing connection to debugger. initial content not found

I managed to find a solution to the problem. It has to do with outdated app xml config files.
So after importing project from source control, create a new application (eg. TestApp) and run / debug it, which works fine.

Compare the 2 app xml config files. In the new file at the top you will see a line:
application xmlns="http://ns.adobe.com/air/application/1.5"
In the old file I had:
application xmlns="http://ns.adobe.com/air/application/1"

So you can change the old with the new app configuration.