#states with effects (fade, slide)
Please try this. may be it will help you.

**Your Code:**
$form['more_info'] = array(
  '#type' =&gt; 'fieldset',
  '#title' =&gt; t('Additional Information'),
  '#collapsible' =&gt; TRUE,
  '#collapsed' =&gt; TRUE,

  // Expand the expand_more_info fieldset if the box is checked.
  '#states' =&gt; array(
    'expanded' =&gt; array(
      ':input[name="expand_more_info"]' =&gt; array('checked' =&gt; TRUE),
    ),
  ),
);


Instead of that you can try it in another way which is mentioned below in hook_form_alter() function.

Example:

$form['more_info'] = array(
                          '#type' =&gt; 'fieldset',
                          '#title' =&gt; t('Additional Information'),
                          '#collapsible' =&gt; TRUE,
                          '#collapsed' =&gt; TRUE,
                     );

**$form['more_info']['und']['#states']**= array(
                                'expanded' =&gt; array(
                                 ':input[**name="expand_more_info[und]**"]' =&gt; array('checked' =&gt; TRUE),
                                ),
                             );


Note: you can use 'visible' instead of 'expanded'.
you can try this in your custom module or template.php