The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).

     var EmployeeID = '<%= Session["EmployeeID"] %>';

Step-1 Remove the "=" sign from the tag and replace it with a "#" sign.

         var EmployeeID = '<%# Session["EmployeeID"] %>';

Step-2 Write "Page.Header.DataBind();" in the Page_Load Event of your page.

Now, it will work perfectly.

Thanks Shibashish Mohanty