You Need to Change your Javascript Like This...
one more thing in url1 you write
"new Employee.aspx....."
here if you have that page placed in side new folder then wirte like this
new/Employee.aspx....
or if you write it for new window then no need to write it just use my provided js function to call your edit method...
<script type="text/javascript" language="JavaScript">
function openph(img) {
var url1 = "Employee.aspx?ResponseType=Edit&Id=" + img.text;
newWindow = window.open(url1, "test", this.target, "top=0,left=0,menubar=no,toolbar=no,location=no, resizable=no,height=550,width=440,status=no,scrollbars=no,minimizable=no,maxmizable=no,resizable=0,titlebar=no;");
if (newWindow.focus()) {
newWindow.focus()
}
}
and you need to change your design code like this...
<asp:imagebutton id="Edit" imageurl="~/edit.png" width="10px" height="10px" runat="server" commandname="<%# Eval("ID") %>" text="<%# Eval("ID") %>" xmlns:asp="#unknown">
OnClientClick="return openph(this)" />
</asp:imagebutton>
if you pass your image button using this then no need to do document.getElementByID and also you do it in wrong way, because when you need to get the element decalred as a item template inside grid or any other control at that time you can not get that element directly...
here you pass this keywork while calling your edit method so you can get that control directly to your caller function so use that...