502 Bad Gateway服务器返回无效或不完整的响应。

Question

when i am trying to submit this function save() this shows "502 Bad Gateway The server returned an invalid or incomplete response. "we didn't do any changes recently in this existing working code. is this a code error or miss configuration of server? why i geting this error.?

function save()
{


    $data = array('client_email' => $this->input->post('client_email'),'client_fname' => $this->input->post('client_fname'),'client_sname' => $this->input->post('client_sname'),'client_company' => $this->input->post('client_company'),'client_phone' => $this->input->post('client_phone')
);


 $our_current_client = $this->input->post('currenct_client');
  $this->order2model->form_update($data,$this->input->post('currenct_client'));

    $other_services_var = '';
    $count_otherss = 0;

    if($this->input->post('otherservices')!='')
    {
        $otherservices = $this->input->post('otherservices');
        $other_id = explode('_',$otherservices);

        $other_services_var = $other_id[1];

        $this->session->set_userdata('service', $other_id[1]);
    }




    if($other_services_var != '')
    {
        //$this->session->set_userdata('service', 'others_radio');
    }
    else
    {
        $this->session->set_userdata('service', $this->input->post('rb'));

        $this->session->unset_userdata('cull');
            $this->session->unset_userdata('cull_max');
            $this->session->unset_userdata('cull_min');
            $this->session->unset_userdata('cull_images');
            $this->session->unset_userdata('lr_image_sub');
            $this->session->unset_userdata('lr_image_del');

            $this->session->unset_userdata('strength');
            $this->session->unset_userdata('strength_images');
    }

    $rb = $this->input->post('rb');
    if($rb=='wed_custom')
    {

        $cull =  $this->input->post('cull_onoffswitch');
        $strength = $this->input->post('str_onoffswitch');
        $this->session->set_userdata('total_images_lr', $this->input->post('total_images_lr'));
        $this->session->set_userdata('lr_image_sub', $this->input->post('lr_image_sub'));
        $this->session->set_userdata('lr_image_del', $this->input->post('lr_image_del'));

        if($cull=='on')
        {
            $this->session->set_userdata('cull', $this->input->post('cull_onoffswitch'));
            $this->session->set_userdata('cull_max', $this->input->post('cull_max'));
            $this->session->set_userdata('cull_min', $this->input->post('cull_min'));
            $this->session->set_userdata('cull_images', $this->input->post('cull_images'));
            $this->session->set_userdata('lr_image_sub', $this->input->post('lr_image_sub'));
            $this->session->set_userdata('lr_image_del', $this->input->post('lr_image_del'));
        }else{
            $this->session->unset_userdata('cull');
            $this->session->unset_userdata('cull_max');
            $this->session->unset_userdata('cull_min');
            $this->session->unset_userdata('cull_images');

        }
        if($strength=='on')
        {
            $this->session->set_userdata('strength', $this->input->post('str_onoffswitch'));
            $this->session->set_userdata('strength_images', $this->input->post('strength_images'));
            $this->session->set_userdata('total_images_lr', $this->input->post('total_images_lr'));
            $this->session->set_userdata('lr_image_sub', $this->input->post('lr_image_sub'));
            $this->session->set_userdata('lr_image_del', $this->input->post('lr_image_del'));

        }else
        {
            $this->session->unset_userdata('strength');
            $this->session->unset_userdata('strength_images');

        }

    }

    $this->session->set_userdata('client_fname', $this->input->post('client_fname'));
    $this->session->set_userdata('client_sname', $this->input->post('client_sname'));
    $this->session->set_userdata('client_company', $this->input->post('client_company'));
    $this->session->set_userdata('client_phone', $this->input->post('client_phone'));
    $this->session->set_userdata('client_email', $this->input->post('client_email'));
    $this->session->set_userdata('rush', $this->input->post('onoffswitch'));
    $this->session->set_userdata('no_images', $this->input->post('no_images'));
    $this->session->set_userdata('file_format', $this->input->post('file_format'));
    $this->session->set_userdata('notes', $this->input->post('notes'));
    $this->session->set_userdata('active_tab', $this->input->post('active_tab'));
    $this->session->set_userdata('current_checked', $this->input->post('current_checked'));
    $this->session->set_userdata('our_client', $our_current_client);
    $this->session->set_userdata('item_details', $this->input->post('item_details'));
redirect('order3');

}