一个脚本在本地运行正常，demo.pyspider.org上运行就失败

[E 151210 02:17:30 base_handler:195] HTTP 521: Unknown

    Traceback (most recent call last):

      File "/opt/pyspider/pyspider/libs/base_handler.py", line 188, in run_task

        result = self._run_task(task, response)

      File "/opt/pyspider/pyspider/libs/base_handler.py", line 167, in _run_task

        response.raise_for_status()

      File "/opt/pyspider/pyspider/libs/response.py", line 190, in raise_for_status

        raise http_error

    HTTPError: HTTP 521: Unknown