在退出 VN Trader 时出错：
Traceback (most recent call last):
File "d:\vnstudio\lib\site-packages\vnpy\trader\ui\mainwindow.py", line 269, in closeEvent
self.main_engine.close()
File "d:\vnstudio\lib\site-packages\vnpy\trader\engine.py", line 232, in close
gateway.close()
File "d:\vnstudio\lib\site-packages\vnpy\gateway\oes\oes_gateway.py", line 223, in close
self.md_api.exit()
RuntimeError: invalid argument: invalid argument
请问这是什么原因所致？该怎么办？
