Namespace Manager or XsltContext needed. This query has a prefix,

Her er min løsning

Som det nok kan ses, så er det bare test.

Imports System.Xml
Partial Class Default2
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
   

        ' Create a namespace manager:
        Dim nt As New NameTable
        Dim nsManager As New XmlNamespaceManager(nt)
        nsManager.AddNamespace("xml", "http://www.w3.org/XML/1998/namespace")
        nsManager.AddNamespace("d", "schemas.appdev.com/grocery")

        SelectNodesWithXPath("//xml:books//@name", nsManager)

       
    End Sub


    Private Sub SelectNodesWithXPath( _
  ByVal name As String, ByVal nsManager As XmlNamespaceManager)

        If Not String.IsNullOrEmpty(name) Then
            Dim doc As New XmlDocument()

            doc.Load("k:\Projects\WorkingWithXML\xml\XMLFile.xml")
            Dim nodeList As XmlNodeList = doc.SelectNodes(name, nsManager)
            For Each node As XmlNode In nodeList
                DropDownList1.Items.Add(node.InnerText)
            Next
        End If
    End Sub


End Class


<?xml version="1.0" encoding="utf-8" ?>
<Test
  xmlns:xsl="schemas.appdev.com/names"
  xmlns="schemas.appdev.com/grocery"
  >

  <xml:myRoot>
    <xml:books name="test1">
      <xml:book>
        hest
      </xml:book>
    </xml:books>
    <xml:books name="test2">
      <xml:book>
        hest2
      </xml:book>
    </xml:books>
    <xml:books name="test3">
      <xml:book>
        hest3
      </xml:book>
    </xml:books>
  </xml:myRoot>
</Test>