crear tag unico xml

Private Sub btnCrearTagUnico_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCrearTagUnico.Click
        Dim doc As New XmlDocument
        doc.Load("tagunico.xml")
        Dim x As XmlNode = doc.SelectSingleNode("/configuration/system.web")
        Dim child As XmlElement = doc.CreateElement("httpRuntime")
        child.SetAttribute("maxRequestLengt", 0)
        x.AppendChild(child)
        doc.Save("tagunico.xml")
        Dim p1 As String = ""
    End Sub


<?xml version="1.0"?>
<configuration>
  <system.web>
    <httpModules>
      <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
    </httpModules>
  </system.web>
</configuration>

<?xml version="1.0"?>
<configuration>
  <system.web>
    <httpModules>
      <add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
    </httpModules>
<httpRuntime maxRequestLengt="0" />
  </system.web>
</configuration>



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