I posted this in the flex issue but it might be an install issue. I have tried uninstalling, rebooting and reinstalling. I get this error on Alerts for mx.controls.Alert. and all the Flex documentation states that its mx.controls.Alert. even in 4.5.
Multiple markers at this line:
-1172: Definition mx.controls:Alert could not be found.
-The import Alert could not be found.
I belive this is an install issue of some kind...
Create new project (if you dont have) then: