actionscript 3 - flex 3.4 compile error when using FileReference object -

when using flex filereference, in flex 3.4, met problem. follows code:

public function save_click():void {

             var systemfilereference:filereference = new filereference();               systemfilereference.save("test","testfile.txt");          } 

but compile fails" invoke undefined method save in filereference), not know why in flex3.4 filereference not support save() method?

you need target flash player 10.