Displayling list of Custom Post Type Posts

If ‘Partners’ is a custom post type, then why don’t you use get_posts? Try using it…

$pages = get_posts(array('post_type' => 'partners', 'posts_per_page'=> -1, 'post_status' => 'publish'));
echo '<select name="activitymeta_sel" id="activitymeta_sel">';
echo '<option value="">Select Partners</option> ';

foreach ( $pages as $page ) {
   $option = '<option value="' . $page->post_title . '">';
   $option .= $page->post_title;
   $option .= '</option>';
   echo $option;
  }
 echo '</select>';

Try this. This should work.