div does not render when asp:Panel Visible=false

When you set the visibility of a control to false, it will not be added to the Page Tree thus it will not be rendered. However, you can use Javascript to set the visibility to false, in this way, you can access to this container on the client side.

divPanel1.Style["display"] = "none";

Referenced from: http://forums.asp.net/t/1302512.aspx/1