I create my fxp file in catalyst and then I import the file into FB4. Everything works fine until I click on "Add/Change property type" and convert it to and air applications. Suddenly I get no UI. I have changed the <s:Application></s:Application> to <s:WindowedApplication></s:WindowedApplication> but still all I get is a blank flash window. Any Ideas?
That's pretty clearly a bug in Flash Builder's Design View. This probably has the same root cause as FB-20120. Try closing and reopening the project.