It looks like this is because the validation for the secondary contact is still being applied. Find this line:
$WAFV_Errors .= WAValidatePN((isset($_POST["Contact_me_Contact_Information_Secondary_Contact"])?$_POST["Contact_me_Contact_Information_Secondary_Contact"]:"") . "",false,true,true,5);
and change it to this:
$WAFV_Errors .= WAValidatePN((isset($_POST["Contact_me_Contact_Information_Secondary_Contact"])?$_POST["Contact_me_Contact_Information_Secondary_Contact"]:"") . "",false,true,false,5);