flash.Vector requires Flash 10+.

std/haxe/Vector.hx

@@ -21,7 +21,7 @@
  */
 package haxe;
 	
-private typedef VectorData<T> = #if flash9
+private typedef VectorData<T> = #if flash10
 	flash.Vector<T>
 #elseif neko
 	neko.NativeArray<T>
@@ -128,4 +128,4 @@ abstract Vector(VectorData<T>)<T> {
 			vec.set(i, array[i]);
 		return vec;
 	}
-}
+}