Form Validation. Ensure Placeholder is not submitted value
In your code these two lines may make issue. remove/comment these lines and try.

$form['field_first_name']['und'][0]['value']['#attributes']['onblur'] = "if (this.value == '') {this.value = 'First Name';}";
$form['field_first_name']['und'][0]['value']['#attributes']['onfocus'] = "if (this.value == 'First Name') {this.value = '';}";