The error is 1000: Ambiguous reference to setStyle. It took me a while to find a solution, It happens when you are trying to set a style, for example: setStyle(”w”,50) in Flex and at the same time you are using the mx_internal namespace. For Example

use namespace mx_internal;
private function dummyTest():void
{
var mainSelector:CSSStyleDeclaration 
          = StyleManager.getStyleDeclaration("VadexTabBar");
if(!mainSelector)
{
mainSelector = new CSSStyleDeclaration();
}
mainSelector.defaultFactory=function():void
{
 
}
mainSelector.setStyle("tabWidth",500);
StyleManager.setStyleDeclaration("VadexTabBar",mainSelector,false);
}

Solution to the Problem:
Instead of opening all the namespace and having “use namespace mx_internal” on top, just selectively open up the namespace “mx_internal::property”, and don’t include use namespace mx_internal on top.For example

private function set navItemFactoryInternal(value:Class):void
		{
			mx_internal::navItemFactory =new ClassFactory(value);
		}