showing save file dialog in client side

Hi

in my Silverlight webapplication I have a button for save a file in client machine,including the following code,when I run it on my local machine it works fine,but when I Publish website and run it via iis (internet information service) app run but when I click button It does not work ,does not show any save file dialog or open file dialog,

can anyone assistance me?

thanks in Advance.

SaveFileDialog objSFD = new SaveFileDialog() { DefaultExt = "xml", Filter = "Excel XML (*.xml)|*.xml", FilterIndex = 1 };
        if (objSFD.ShowDialog() == true)
        {}