jQuery Validation at least one checkbox is selected

Answer 1

You will have to change the name attributes of the checkboxes, and add a rule for it with the minlength set to 1.

You can after show the custom message and append it to #error_msg3 with :

if(element.attr("name") == "check") error.appendTo("#error_msg3")

EDIT

$("input[type='checkbox'][name='check']").change(function() {
    if ($("input[type='checkbox'][name='check']:checked").length){
        $(this).valid()
    }
})

EDIT 2

I've updated the Fiddle, now the message toggles correctly when you have at least one checkbox checked or not.

$("input[type='checkbox'][name='check']").change(function() {
    $('#submitDetails').valid();
});

Fiddle here