Using Yahoo Shopping Web Services

Hi,
I am using this sample code :

protected void Page_Load(object sender, EventArgs e)
{
string xmlDocument = @"http://shopping.yahooapis.com/ShoppingService/v3/productSearch?appid=[@AppId]&query=perfume";

DataSet yahooResult = RetrieveXMLDocument(xmlDocument);

GridView1.DataSource = yahooResult.Tables[0];
GridView1.DataBind();
}

I am putting my real AppId to @AppId place.
but instead of result XML document I am getting "Message :User-agent not valid "

What can be the solution? Thanks!