GDI+ 中发生一般性错误

public static string CreateDirectory(string str)

    {

        if (!Directory.Exists(HttpContext.Current.Server.MapPath(str)))//如果不存在就创建str文件夹

        {

            Directory.CreateDirectory(HttpContext.Current.Server.MapPath(str));

        }

        return str;

    }

try

        {

            string base64 = context.Request["base64"].Trim().ToString();　　　　　　//接收前台传过来的参数

            byte[] btsdata = Convert.FromBase64String(base64);

            string ImgName = Guid.NewGuid().ToString("D") + ".jpg";

            string uploadDir = OA_Class.CreateDirectory("~/images/Shipping/" + DateTime.Now.Year + "/") + ImgName;

            using (System.Drawing.Image img = System.Drawing.Image.FromStream(new System.IO.MemoryStream(btsdata)))

            {

                img.Save(uploadDir, System.Drawing.Imaging.ImageFormat.Jpeg);//GDI+ 中发生一般性错误

            }

            context.Response.Write(base64);

        }

        catch (Exception ex)

        {

            LogHelper.WriteLog("Image.ashx", ex);

        }