title: AppendChild and Specified method is not supported exception
body: <p>Below code gives this error message "Specified method is not supported". But <a href="http://msdn.microsoft.com/en-us/library/ms163342.aspx?appId=Dev10IDEF1&amp;l=en-US&amp;k=k(SYSTEM.XML.XPATH.XPATHNAVIGATOR.APPENDCHILD);k(TargetFrameworkMoniker-%22.NETFRAMEWORK&amp;k=VERSION=V4.0%22);k(DevLang-CSHARP)&amp;rd=true" rel="nofollow noreferrer">here</a> is sample which is same with mine.</p>
  
  <pre><code>        FileInfo file = new FileInfo("../../file.xml");
          XDocument xfile = XDocument.Load(file.FullName);
          XPathNavigator nav = xfile.CreateNavigator();
  
          nav.AppendChild("&lt;pages&gt;100&lt;/pages&gt;");
  </code></pre>