[jQuery] [jQuery Validate] One error message for multiple invalid elements

[dannet]

Hello I'm using the jquery validate plugin from bassistance.de. In my
form I have 3 select (day, month and year) to determine the birth date
of the user (the 3 inputs are used as independent fields). My problem
is that when I validate it, if the user has not entered the day, month
of year, I get obviously 3 error messages, and I need to display a
unique error message for the 3 select elements.

I have created a span id "error_date" and I'm using this code to place
the messages after the year select, I just need to show it once:

        errorPlacement : function(label, element) {
                if (element.attr("id") == "day" || element.attr("id") == 
"month" ||
element.attr("id") == "year") {
                        label.appendTo("#error_date");
                } else {
                        label.insertAfter(element);
                }
        },

I have tried with label.html("#error_date") with no results.

Thanks in advance
Regards
Daniel