微信支付二维码本地测试可以，上传到服务器不显示问题

  protected void Page_Load(object sender, EventArgs e)
        {
            if (Session["code"]!=null)
            {
                string str = Session["code"].ToString();

                QRCodeEncoder qrCodeEncoder = new QRCodeEncoder();
                qrCodeEncoder.QRCodeEncodeMode = QRCodeEncoder.ENCODE_MODE.BYTE;
                qrCodeEncoder.QRCodeErrorCorrect = QRCodeEncoder.ERROR_CORRECTION.M;
                qrCodeEncoder.QRCodeVersion = 0;
                qrCodeEncoder.QRCodeScale = 4;

                //将字符串生成二维码图片
                //将字符串生成二维码图片
                Bitmap image = qrCodeEncoder.Encode(str);

                //保存为PNG到内存流  
                MemoryStream ms = new MemoryStream();
                image.Save(ms, ImageFormat.Png);
                Response.ClearContent();

                Response.ContentType = "image/Png";
                //输出二维码图片
                Response.BinaryWrite(ms.GetBuffer());
                Response.End();
            }
        }