How to use custom modal with ctools and triggered by a button form
Try this:

  $form['ajax_button'] = array(
    '#type' =&gt; 'button',
    '#value' =&gt; t('New Post'),
    '#attributes' =&gt; array('class' =&gt; array('ctools-use-modal','ctools-modal-slogan-style')),
    '#id' =&gt; 'hs-ajax-button',
    );


Vincent