reading data from excel files

Yesterday i got a requirement as follows

As in the screen shot depending
 upon the selection in the radio
 button list I need to fill drop down,
 similar to cascading drop down lists 

I used Jquery ajax to call database.
 Following steps are used in
 developing functionality

Step 1

Add using System.Web.Services; in the name space region 

Add attribute [WebMethod] above the method to fill data.

example [WebMethod]
function filldropdown()
{
// do db interaction to get data
}



Step 2

Add following javascript to web page

            $(document).ready(function () {



                $('#<%= rdbFormType.ClientID%> :input').click(function () {

                   

                  var selRad = $("input[@name=<%=rdbFormType.ClientID%>]:radio:checked").val();

                    if (selRad == 1) {
                       $('#AssociatedForm').
css('visibility', 'visible');
                        var loc = window.location.href;

                        loc = (loc.substr(loc.length - 1, 1) == "/") 
? loc + "AddForm.aspx" : loc;
       $.ajax({
      type: "POST",
                            url: loc + "/" + 'methodname',
     data: "{}",


 beforeSend: function (xhr) {
            xhr.setRequestHeader("Content-type",
                "application/json; charset=utf-8");
                            },
    dataType: "json",
                            success: function (msg) {

 $('#<%= ddlForm.ClientID%>')
.get(0).options.length = 0;
                                $('#<%= ddlForm.ClientID%>')
.get(0).options[0] = new Option("Select Form", "-1");

                                $.each(msg.d, function (index, item) {
                                    $('#<%= ddlForm.ClientID%>').get(0).options[$('#<%= ddlForm.ClientID%>').get(0).options.length] =
 new Option(item.Display,item.Value);
                                });
                            },
                            error: function (res, status, ex) {
                               
                                alert('Not able to load Form Data');
                            }



                        });

                      

             }
                 else {
                      $('#AssociatedForm').css('visibility', 'collapse');
                   }

               });

            });  
      
Step 3 Add following to the web.config


add name="ScriptModule" 
type="System.Web.Handlers.ScriptModule, 
System.Web.Extensions, Version=1.0.61025.0,
 Culture=neutral, 
PublicKeyToken=31bf3856ad364e35"


In following above steps you may encounter following errors

Error 1) 500 internal server error while posting data to server 

fix : replace data: "{}" with data: {}

Error 2) 200 +ok but it will return whole html design. 

Fix: check your database calling method is having keywords 
Public and static and also check whether step 3 is followed or not

Error 3)Invalid postback or callback argument.
A Event validation is enabled using 
 
in configuration or <%@ Page EnableEventValidation=”true” %> in a page.
 Â For security purposes,
 this feature verifies that arguments to 
postback or callback events originate 
from the server control that originally rendered them.
 Â If the data is valid and expected, 
use the ClientScriptManager.
RegisterForEventValidation method 
in order to register the postback 
or callback data for validation.

Fix: protected override 
void Render(HtmlTextWriter writer)
{
Page.ClientScript.
RegisterForEventValidation
(dropdownlistcontrol.UniqueID, value);


base.Render(writer);
}