How to store date_popup fileld in mysql
Node Field must be expecting date field value in unixtimestamp format while the custom form will return the value in the format mention as '#date_format' => 'Y-m-d'. View of your form submit values will look like.



You should run the submit date value through strtotime() to get the unxtimestamp value for it before assigning it to node field.

$node_wrapper-&gt;field_due_date6-&gt;set(strtotime($form_state['values']['comment_date']));