C# downloader problem at linkl

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C#

I try to create a downlaoder in c# wich crashes because of an error i dont understand. i got the code from another site and copied it exactly to try it out but it doesnt work for me. my script:

private void button4_Click(object sender, EventArgs e)
       {
               progressBar.Visible = true;
               WebClient webClient = new WebClient();
               webClient.DownloadFile("http://www.spadille.net/aos075install.msi", @"C:\aos075install.msi");
               webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged);
               webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
               private void ProgressChanged(object sender, DownloadProgressChangedEventArgs e)
                   {
                       progressBar.Value = e.ProgressPercentage;
                   }

               private void Completed(object sender, AsyncCompletedEventArgs e)
                   {
                       MessageBox.Show("Download Abgeschlossen!");
                       progressBar.Visible = false;
                       System.Diagnostics.Process.Start("\\aos075install.msi");
                   }

               private void button5_Click(object sender, EventArgs e)
                   {
                       System.Diagnostics.Process.Start("\\Ace of Spades\\readme.txt");
                   }

       }

the link to the original:
http://www.csharp-examples.net/download-files/[^]

thanks for help!

Sorry for not posting the exact error but its in german so it wont help most of you, but if i translate it it's like: Unhandled WebException - Exceptional Error During a Web cleint demand.