About (500) Internal Server Error in WebClient

Hi all,
The following code 

WebClient wc = new WebClient();
string output = wc.DownloadString(new Uri("http://www.cnutg.com"));
always returns an error of "The remote server returned an error: (500) Internal Server Error."
 The code function normally if I use it to access other website. But I can't do it when it is used to access "http://www.cnutg.com".
Could anyone figure out the reason behind?
Thanks
Xavier Chan

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