Add close button in ctools model dialog
As for this issue commited on November '11, you should be able to close any CTools modal window with a link that has the class "ctools-close-modal"

For example, in my modal I've got this for element to cancel and close:

  $form['actions']['cancel'] = array(
    '#markup' =&gt; l(t('Cancel'), '#',
       array(
         'attributes' =&gt; array(
           'class' =&gt; 'ctools-close-modal'
          ),
         'external' =&gt; TRUE
       )
     )
  );