无法获取ncname和netbiosname属性

我在网上有一些关于检索一个active directory域的netbiosname(windows 2000以前的域名)的代码。这是我的代码示例:

Me._rootDSE = New System.DirectoryServices.DirectoryEntry("GC://RootDSE", "", "")
      Dim results As System.DirectoryServices.SearchResultCollection = Nothing
      Dim ADSPath As String = "GC://CN=Partitions," + Me._rootDSE.Properties("configurationNamingContext").Value.ToString()

      Dim adse As System.DirectoryServices.DirectoryEntry = New System.DirectoryServices.DirectoryEntry(ADSPath, "", "")

      Dim searcher As System.DirectoryServices.DirectorySearcher

      searcher = New System.DirectoryServices.DirectorySearcher(adse)
      searcher.SearchScope = DirectoryServices.SearchScope.OneLevel
      searcher.Filter = "(&(objectClass=crossRef)(systemflags=3))"
      searcher.PropertiesToLoad.Add("netbiosname")
      searcher.PropertiesToLoad.Add("ncname")

      results = searcher.FindAll()

      If results.Count > 0 Then
        For Each sr As System.DirectoryServices.SearchResult In results
          Dim de As System.DirectoryServices.DirectoryEntry = sr.GetDirectoryEntry()
          'netbiosname and ncname properties returns nothing
          System.Diagnostics.Trace.WriteLine(sr.GetDirectoryEntry().Properties("netbiosname").Value.ToString())
          System.Diagnostics.Trace.WriteLine(sr.GetDirectoryEntry().Properties("ncname").Value.ToString())
        Next
      End If

当我使用“(&objectClass=crossref)(systemflags=3)”筛选器时,不会得到任何结果,但当我删除systemflags筛选器时,会得到一些结果。

但是,在我得到的搜索结果中,我仍然无法访问ncname和netbiosname属性的值。我可以正确地获得其他属性,比如搜索结果的distinguishedname和cn。

你知道我可能做错了什么吗,或者去哪里看?