JQuery validation checkbox error/valid issue

I've hit upon a problem with my newsletter checkboxes...I have two options sign up for one or other or both. Upon validating only the top checkbox receives the class="error" or class="valid" they both have the same name, however, when I check the bottom one it makes the top one valid. How can I include both checkboxes with the error/valid class as my error placement is shown by the checkbox borders turning red. Any help would be greatly appreciated.

html

<input type="checkbox" id="interested_in[future]" name="interested_in[]" value="future">
<input type="checkbox" id="interested_in[print]" name="interested_in[]" value="print">

jQuery

 $(function(){jQuery.validator.setDefaults({
            errorContainer: '.validation-advice',
            errorPlacement: function(error, element) {
                    error.appendTo('.validation-advice');

            },
      });

    $('#subscribe').validate({
              rules: {               
                  web_user_email: { 
                    required:   true,
                    email:      true
                 },
                 "interested_in[]": {
                    required:   true,
                    minlength: 1
                 }
              }, etc.....