It may sound silly I know, but it looks like I'm not able to use Alert messages...
I built an extension using Flash Builder and Extension Builder and sometimes I simply use "Alert.show('Muy message')" in order to quickly debug some value but within the extension I can't see anything.
What's the matter with this?
Try this: Alert.show("My Message", "Title", Alert.OK, Sprite(mx.core.Application.application));
It's kind of hidden, but the docs explain this in the "Bringing up Alert dialogs from an extension" section, which you can find here: http://cssdk.host.adobe.com/sdk/1.0/docs/WebHelp/programmers_guide/customizing_the_ui.htm.