How to add comment to a node with ajax (ctools modal)?
You need to add ajax library to that

drupal_add_library('system', 'drupal.ajax');


Or you can use the below function to render the ajax link 

$block['content'] = l(t('Add a review'), "add/nojs/review/{$comment_site_id }", array('html' =&gt; TRUE, 'attributes' =&gt; array('class' =&gt; "ctools-use-modal ctools-modal-first-popup-style")));


Replace the above line to below.

$block['content'] = ctools_modal_text_button(t('Newsletter datacapture modal'), "add/nojs/review/{$comment_site_id }", t('Add a review'), "ctools-modal-first-popup-style");


Modify the argument 

function current_posts_menu() {
 $items['add/%ctools_js/review/%'] = array(
   'page callback'    =&gt; 'current_posts_ctools_modal_review',
   'page arguments'   =&gt; array(1,3),
   'access arguments' =&gt; array('create review content'),
 );
 return $items;
}


and not to mention "Clear Cache"