xmldocument.selectnodes not working

<?xml version="1.0" encoding="utf-8"?>

<feed xmlns="http://www.w3.org/2005/Atom" xmlns:creativeCommons="http://backend.userland.com/creativeCommonsRssModule" xmlns:thr="http://purl.org/syndication/thread/1.0">

  <title type="html">StackOverflow.com - Questions tagged: c</title>

  <link rel="self" href="http://stackoverflow.com/feeds/tag/c" type="application/atom+xml" />

  <subtitle>Check out the latest from StackOverflow.com</subtitle>

  <updated>2008-08-24T12:25:30Z</updated>

  <id>http://stackoverflow.com/feeds/tag/c</id>

  <creativeCommons:license>http://www.creativecommons.org/licenses/by-nc/2.5/rdf</creativeCommons:license>

  <entry>

    <id>http://stackoverflow.com/questions/22901/what-is-the-best-way-to-communicate-with-a-sql-server</id>

    <title type="html">What is the best way to communicate with a SQL server?</title>

    <category scheme="http://stackoverflow.com/feeds/tag/c/tags" term="c" />

    <category scheme="http://stackoverflow.com/feeds/tag/c/tags" term="c++" />

    <category scheme="http://stackoverflow.com/feeds/tag/c/tags" term="sql" />

    <category scheme="http://stackoverflow.com/feeds/tag/c/tags" term="mysql" />

    <category scheme="http://stackoverflow.com/feeds/tag/c/tags" term="database" />

    <author>

      <name>Ed</name>

    </author>

    <link rel="alternate" href="http://stackoverflow.com/questions/22901/what-is-the-best-way-to-communicate-with-a-sql-server" />

    <published>2008-08-22T05:09:04Z</published>

    <updated>2008-08-23T04:52:39Z</updated>

    <summary type="html">&lt;p&gt;I am going to be using c/c++, and would like to know the best way to talk to a MySQL server.  Should I use the library that comes with the server installation?  Are they any good libraries I should consider other than the official one?&lt;/p&gt;</summary>

    <link rel="replies" type="application/atom+xml" href="http://stackoverflow.com/feeds/question/22901/answers" thr:count="2"/>

    <thr:total>2</thr:total>

  </entry>

</feed>

To Get select node

  XmlDocument doc = new XmlDocument();

  XmlNamespaceManager nsmgr = new XmlNamespaceManager(doc.NameTable);

  nsmgr.AddNamespace("atom", "http://www.w3.org/2005/Atom");

 doc.Load(feed); 

            // successful

  XmlNodeList itemList = doc.DocumentElement.SelectNodes("atom:entry", nsmgr);