jquery ui Dialog: cannot call methods on dialog prior to initialization

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.