asp.net controlIDs
===

I have the following code:

    <script type="text/javascript">    
    
        Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(beginRequestHandle);
        Sys.WebForms.PageRequestManager.getInstance().add_endRequest(endRequestHandle);
        function beginRequestHandle(sender, Args) {
            //Do something when call begins. 
    
            document.getElementById("btn1").style.visibility = "hidden";
            document.getElementById("btn2").style.visibility = "hidden";
        }
    
        function endRequestHandle(sender, Args) {
            if (document.getElementById('<%= hfResultsCount.ClientID %>').value != 0) {
                document.getElementById("btn1").style.visibility = "visible";
                document.getElementById("btn2").style.visibility = "visible";
            }
            else {
                document.getElementById("results").innerHTML = "<br><b><center><font style='font-family:Haettenschweiler; font-size:xx-large'>No data found, please try again.</b></font></center>";
            }
        }
    </script>

and the code for btn2:

     <input type="button" runat="server" name="btn2" id="btn2" value="New Window"
     style="visibility:hidden;font-weight:bold;width:200" onclick="window.open('http://microsoft.com');" />

I am using Js to show/hide buttons (needs to be done like this so don't suggest otherwise) and while `btn1` is `asp:button` it always works but for `<input type=button>` I keep getting this error

    Microsoft JScript runtime error: Unable to get value of the property 'style': object is null or undefined

The way to fix that for `btn1` was to just add `ClientID=Static` but how to do that for `<input>` button? (I do not want to make it asp:button since I need it to not postback)

Everything is in an UpdatePanel with ClientID=Static also.

I know its something to do with the IDs and the master page since it works fine on a page on its own.