showing save file dialog in silverlight 5

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C#

Hi I implement a web application in Silverlight 5,I have a button including following code for save a file in client side, it works fine in all browsers in local machine, but when I locate that in a host and refer to website for visit it, application works,but save file dialog does not be show, how can I solve that?
Thanks

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