Proxy Authentication Required

I am trying to get the XML from a URL but I'm getting the following error.

Proxy Authentication Required.

Here is the code I am using:

string sUrl = "http://google.com";

StringBuilder oBuilder = new StringBuilder();

StringWriter oStringWriter = new StringWriter(oBuilder);

XmlTextReader oXmlReader = new XmlTextReader(sUrl);

XmlTextWriter oXmlWriter = new XmlTextWriter(oStringWriter);

while (oXmlReader.Read())

{

oXmlWriter.WriteNode(oXmlReader, true);

}

addListItem( oBuilder.ToString() );

oXmlReader.Close();

oXmlWriter.Close();