How to get SPUser name from User Id?

string userName= web.AllUsers.GetByID(Convert.ToInt32(userid)).Name;

http://firstblogofvarun.blogspot.com/2009/03/how-to-get-spuser-name-from-user-id.html

Request failed with HTTP status 417: Expectation failed

In Web.config
<system.net>
    <defaultProxy enabled="true" useDefaultCredentials="true">
      <proxy proxyaddress="http://192.168.22.11:3118" bypassonlocal="True" usesystemdefault="True" />
    </defaultProxy>
    <settings>
      <servicePointManager expect100Continue="false" />
    </settings>
  </system.net>

 

http://symmetri.blogsome.com/2008/09/01/request-failed-with-http-status-417-expectation-failed/

http://social.msdn.microsoft.com/Forums/en-US/devdocs/thread/60cd6e6a-4157-4811-8ed3-1e46f9022ea8