C# Checking for valid URL

[ninjatruck]

I am trying to write a web app that will check to see if a given URL is valid. This is the code i have so far:

WebRequest wr = WebRequest.Create(url);
        wr.Method = WebRequestMethods.Http.Head;
        try
        {
            using (HttpWebResponse response =   (HttpWebResponse)wr.GetResponse())
            {
                Label1.Text = (response.StatusCode.ToString());
            }
        }

        catch (Exception)
        {
            Label1.Text = ("Invalid URL");

        }

It works for checking if http://www.google.com, Label1 reads "OK" after, and it also works with a non existent page, such as http://www.google.com/notapage, but I'm trying to check to see if, for example, "http://www.amazon.com/exec/obidos/ASIN/B000GELXHY" is a valid URL, and after the code is executed, Label1 reads "Invalid URL", even though this is a valid URL.

I am new to C#, so I may be using the wrong class for what I'm trying to do. Any help would be greatly appreciated.

P.S. I don't know if it's relevant, but the code is being executed upon a button click.
P.S.S. replace "url" above with whatever url i am currently testing

[Freon22]

Ok I redid your code a little and it shows good url where it is good and bad url where they return an error 404. I made it a little simpler then yours hope this help. btw could you please post back if this help or even if it doesn't. Thanks

using System.Net;


protected void btnTestURL_Click(object sender, EventArgs e)
    {
        try
        {
            string url = TextBox1.Text;
            if (url != "")
            {
                WebRequest Irequest = WebRequest.Create(url);
                WebResponse Iresponse = Irequest.GetResponse();
                if (Iresponse != null)
                {
                    Label1.Text = "This is a good URL.";
                }
            }
        }
        catch (Exception ex)
        {
            Label1.Text = "This is a bad URL it returns an ERROR 404 >>>>>>>> " + ex.ToString();
        }
    }