Accessing into element of a child symbol with array

Hi, I have this code:

var aXefsA = [];

for (var i = 1; i <= maxXefs; i++) {

     sXefA = sym.createChildSymbol("sXefA", "rXefsList");

     aXefsA[i] = sXefA;

     aXefsA[i].getSymbolElement().css({"position":"fixed"});    

     aXefsA[i].getSymbolElement().css("left",x); //works fine

     sym.getSymbol(aXefs[i]).$("foto").css("background-image",'url('+'images/'+fXefs[i].imatge +')'); //don't work

}

In last line the console show this error: Javascript error in event handler! Event Type = element

I try too:

     sym.getSymbol(sXefA).$("foto").css("background-image",'url('+'images/'+fXefs[i].imatge+') '); //don't work

and:

     var symTest = sym.getSymbol(aXefs[i]);

     sym.getSymbol(symTest).$("foto").css("background-image",'url('+'images/'+fXefs[i].imatge+ ')'); //don't work

but nothing, why?