Arowana, The Flex Viewer Source code zip does not come with the Flex API swc (to keep down on the size of the download). If you read the readme.txt it will explain that you have to download the AGS Flex API swc separately and place it in the libs folder of your project.Don't forget to click the Mark as answer check on this post and to click the top arrow (promote).Follow these steps as shown in the below graphic: