function CallService()   {        var name = $("#taYourName").text(); 

     //Also check whether you're getting the name before you call the webservice

    // alert(name)      $.ajax(       {           Type: "POST",           contentType: "application/json; charset=utf-8",          url: "YourNameIs.asmx/YourName",           data: "{ 'yourName': '"+name+"' }",          success: function (msg) {              $("#lblForAjax").text(msg.d);           }       });

Check below url's you'll have idea..

http://dotnetslackers.com/articles/ajax/using-jquery-with-asp-net.aspx#consuming-a-web-service-using-asp-net-ajax

http://encosia.com/2008/06/05/3-mistakes-to-avoid-when-using-jquery-with-aspnet-ajax/