On an old project I had an annoying problem with Flex builder that meant only the main application’s MXML file would allow me to debug the application. If I tried to debug or run on another file in the project I would get the error, “This file cannot be launched”.
In order to fix this, all you need to do is make sure the folder/package with your files is added to the ‘runnable application files’ in the Flex Applications tab of projects properties. If there are already added, just try adding again and it should resolve the issue.
Thanks to Jason San Jose for pointing this out to me!