xmlwriter not recognised

Hi
I'm looking at an example use of the xmlwriter in .net 2.0.
When I compile the code shown, I get errors like

The type or namespace name 'XmlWriterSettings' could not be found (are you missing a using directive or an assembly reference?)      

Why is this happening please? Do I need to add a reference to the project?

Thanks

<%@ WebHandler Language="C#" Class="Handler" %>
 
using System;
using System.Web;
 
public class Handler : IHttpHandler {
 
    public void ProcessRequest(HttpContext context)
    {
        XmlWriterSettings settings = new XmlWriterSettings();
        settings.Indent = true;
 
        context.Response.ContentType = "text/xml";
 
        using (XmlWriter writer = XmlWriter.Create(context.Response.OutputStream, settings))
        {
            writer.WriteStartElement("slides");
            writer.WriteStartElement("slide");
            writer.WriteAttributeString("imageUrl", "foo.jpg");
            writer.WriteAttributeString("thumbnailUrl", "foo_thumb.jpg");
            writer.WriteAttributeString("caption", "this is a test");
            writer.WriteEndElement();
            writer.WriteEndElement();
        }
    }
 
    public bool IsReusable {
        get {
            return false;
        }
    }
 
}

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