Why this doesn't work _quick question

1 
  var s:String = "Reactor_" + pic + "_" + dif;
            var ClassReference:Class = getDefinitionByName(s) as Class;
            var tempActor1:ClassReference = new ClassReference();
            var tempActor2:ClassReference = new ClassReference();

error:ClassReference type not found.
below works.but i do need the tempActor1/2 be treated as ClassReference type not MovieClip…

  var s:String = "Reactor_" + pic + "_" + dif;
            var ClassReference:Class = getDefinitionByName(s) as Class;
            var tempActor1:MovieClip = new ClassReference();
            var tempActor2:MovieClip = new ClassReference();

why…HELP.