UPDATE: As of January 2012 UDK, WidgetInitialized & Event Listeners are back!
WidgetInitialzied() is not currently working in the Nov 2011 UDK integration of Scaleform 4. It should be in the next release of UDK however, as the fix has been completed but not included in the current release.
Until then, you can use potential workarounds such as ExternalInterface.call() or FSCommands to notify Unreal that a CLIK widget is on the stage. For example:
In ActionScript 3:
//parameter 1 = button instance name
//parameter 2 = button path
//parameter 3 = button instance name (without quotes)
ExternalInterface.call("WidgetInit", "myAS3Button", "this.myAS3Button", myAS3Button);
Then in UnrealScript:
Sorry about that folks.
var GFxObject MyAS3Button;
function WidgetInit(string WidgetName, string WidgetPath, GFxObject Widget)
MyAS3Button = Widget;