Uncaught TypeError: Cannot read property 'getSymbolElement' of undefined

Hi community,

I am tryign to build a new project and I've got an error in console log Uncaught TypeError: Cannot read property 'getSymbolElement' of undefined .

Does any one why is that?

The code is at stage->creationComplete

$.getJSON("content.json",

          function(data){

                    for(var a=0; a<2; a++){

                    var b = sym.getSymbol('menu').createChildSymbol("thumbnail", "doorscontet");

                        b.getSymbolElement().css({"background-size":"contain",

                                           "float": "left",

  });

                    b.$("titleholder").html(data[a].title);

                    b.$("imageholder").css({"background-image":"url('"+data[a]. image+"')",

                                                           "background-size":"cover"

                                            });

                    b.$("imageholder").data('myIndex', a);

                    }

                    });

Thanks in advanced.