Show popup from popup window

Hello there,

In my asp.net application, one of the web page has a small popup(say PopUp1) containing a hyperlink.
Now when user clicks this link, I need to open another popup(say PopUp2) but in Parent Window that hosts the origional PopUp1.
Also, FYI, the PopUp2 that I want to show is currently a user control which I have declared in PopUp1.

If I call below script from PopUp1,

    PopUp2.cs

        public void ShowEmailPreviewPopup()
        {           
            ScriptManager.RegisterStartupScript(ctlEmailPreviewUpdatePanel,
                                ctlEmai ...