DTcms4/5远程图片自动保存报错：A generic error occurred in GDI+.

var htmlSource2 =new JumonyParser().LoadDocument(url).Document.Find("#CPHMain_gvPartSearch_img80_0 > img");
foreach (var htmlElement in htmlSource2)
{
   //保存图片
  string upLoadPath = sysConfig.webpath + sysConfig.filepath + "/myfolder/thumbnail/";
  //站点目录+上传目录
  string fullUpLoadPath = Utils.GetMapPath(upLoadPath); //上传目录的物理路径
  Thumbnail.MakeRemoteThumbnailImage(htmlElement.Attribute("src").Value().Trim(),fullUpLoadPath + model.pn + ".jpg", 300, 300);
  html += string.Format("<tr><td align=\"center\">photo</td><td>{0}</td></tr>",htmlElement.Attribute("src").Value().Trim());
}

if (!Directory.Exists(fullUpLoadPath))
{
    Directory.CreateDirectory(fullUpLoadPath);
}