ASP.Net MVC Error: An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter

Hi,

I am new to MVC and binding a table column{names} to dropdown, but I am facing issue on passing selected value to new string action method and respective view is displaying missing parameter error. I am attaching my code snippet below. Kindly check and let me know your solution.

Controller

    //Binding Dropdown-Working Fine
    public ActionResult Dropdownload()
        {
            EmployeeContext conn = new EmployeeContext();
            var selecteditems = conn.Employees.Select(x=>new {id=x.empid,name=x.empname }).ToList();
            ViewBag.employeelist = new SelectList(selecteditems, "id", "name");
            return View();
        }

        //String action value are passing but displaying error
        public string clickme(int id)
        {
            EmployeeContext conn = new EmployeeContext();
            string selectedname = conn.Employees.Where(x => x.empid == id).Select(x => x.empname).Single();
            return "You selected the name " + selectedname;
        }

View

<script src="~/Scripts/jquery-1.10.2.js">
</script>
<script type="text/javascript">
    $(document).ready(function () {
        $("#btnsubmit").click(function () {
            var id = $("#dropid").val();            
            var data=JSON.stringify({'id':id});
            $.ajax(
                {
                url: '/Employee/Clickme/'+id,
                type: "POST",
                data: data,
                success: function () { alert(data);},
                contentType: 'application/json'
            });
        });
    });
</script>
<div style="font-family:'Franklin Gothic Medium', 'Arial Narrow', Arial, sans-serif">
    @using (Html.BeginForm("Clickme","Employee",FormMethod.Post))
    {
    <h2>Dropdown</h2>
    @Html.DropDownList("ddllist",ViewBag.employeelist as SelectList, "Select Name",new { id="dropid"})
        <input type="submit" value="submit" id="btnsubmit"/>
    }
</div>

Error

Server Error in '/' Application.
The parameters dictionary contains a null entry for parameter 'id' of non-nullable type 'System.Int32' for method 'System.String clickme(Int32)' in 'Learning.Controllers.EmployeeController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter.
Parameter name: parameters