Error 400 Bad Request 如何解决

Response Headers
Server        Zeus/4.3
Date        Fri, 05 Dec 2008 08:45:33 GMT
Connection        close
Content-Type        text/html
Request Headers
Host        220.231.13.100
User-Agent        Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.0.4) Gecko/2008102920 Firefox/3.0.4
Accept        text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language        zh-cn,zh;q=0.5
Accept-Encoding        gzip,deflate
Accept-Charset        gb2312,utf-8;q=0.7,*;q=0.7
Keep-Alive        300
Connection        keep-alive

solve it.
because response header lacks the HOST field.