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On the Preview tab, can you click the "Application URL" link so that it opens in your browser and then add config.xml to the end of the url and load it and let us know what the URL of the operational layer is? Also try loading the operation layer's URL in your browser to see if you get the REST metadata page for it.
1.) Do you have a crossdomain.xml file at http://esri:8080/crossdomain.xml or is your Viewer also on http://esri:8080/ ?
2.) Do you see the ArcGIS REST Services Directory at http://ESRI:8399/arcgis/rest/services/ ?
Here is documentation for the Application builder:
http://resources.arcgis.com/en/help/flex-viewer/concepts/index.html#/Getting_started_with_the_applic...