I have an app on jquery 1.5 with dialogs worked fine. While I have a lot of .live handlers, I changed this to .on. For that, I have to update jquery (now 1.8.3 an jquerui 1.
Try this instead
$(document).ready(function() {
$("#divDialog").dialog(opt).dialog("open");
});
You can also do:
var theDialog = $("#divDialog").dialog(opt);
theDialog.dialog("open");
That's because the dialog is not stored in $('#divDialog'), but on a new div that is created on the fly and returned by the .dialog(opt) function.