I have searched SO & google, but I can't seem to get this to work.
The code is in the codebehind click event of a Cancel button in my asp.net application but does not seem to close the popup window. Any ideas?

try

{

    if (btnCancel.Text == Close)

    {

        String csName1 = PopupScript;

        Type csType = this.GetType();



        ClientScriptManager cs = Page.ClientScript;

        if (!cs.IsClientScriptBlockRegistered(csType, csName1))

        {

            ClientScript.RegisterStartupScript(GetType(), ClosePopup, window.close();, true);

        }

    }

}  

Update: After postback, when I look at the source page, the only code I see related is:

//<![CDATA[

(function() {var fn = function() {$get(ToolkitScriptManager1_HiddenField).value = '';Sys.Application.remove_init(fn);};Sys.Application.add_init(fn);})();window.close();

document.getElementById('ValidationSummary1').dispose = function() {

    Array.remove(Page_ValidationSummaries, document.getElementById('ValidationSummary1'));

}