http://signin.ebay.com/aw-cgi/eBayISAPI.dll 不仅需要用户名和密码作为发布数据，而且其他参数，也许你没有考虑到这一点。使用Firebug上的Net选项卡查看传递的参数，并尝试复制它。

http://signin.ebay.com/aw-cgi/eBayISAPI.dll not only expects username and password as post data, but other parameters as well, maybe you didn't take account of that. Use Net tab on firebug to see the parameters passed, and try to duplicate it.