Twittering with Arduino+Ethernet Shield

I am using my universities network so due to restrictions, I cannot use DHCP to automatically assign the IP hence iam doing it manually.
Ok i declared the DNS server IP:

IPAddress myDns(168, 126, 63, 1);
Ethernet.begin(mac, ip, myDns);

It gives the following result:

117.17.80.199
255.255.255.0
117.17.80.1
168.126.63.1
connecting ...
HTTP/1.0 403 Forbidden
Content-Type: text/html; charset=utf-8
Cache-Control: no-cache
Vary: Accept-Encoding
Date: Thu, 24 Jan 2013 01:19:45 GMT
Server: Google Frontend

Error 403 - Status is a duplicate.
failed : code 403

what might be wrong now?