Sys.Webforms.PageRequestManagerServerErrorException: Object reference not set to an instance of an object.
I was getting this error when I clicked on an object that's inside the UpdatePanel.
The solution was to ..
EnablePartialRendering="true" to "false"
<asp:ScriptManager ID="ScriptManager1" runat="server" ScriptMode="Release" EnablePartialRendering="true">
to
<asp:ScriptManager ID="ScriptManager1" runat="server"
ScriptMode="Release"EnablePartialRendering="false">
