Web Service error Could not create type 'LookUp.LookUpService'.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;

namespace LookUp
{
    /// <summary>
    /// Summary description for LookUpService
    /// </summary>
    [WebService(Namespace = "http://tempuri.com/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem(false)]
    // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
    //[System.Web.Script.Services.ScriptService]
    public class LookUpService : System.Web.Services.WebService
    {

        [WebMethod]
        public string HelloWorld()
        {
            return "Hello World";
        }
    }
}

Server Error in '/LookUp' Application.

Parser Error
  Description: An error occurred during the parsing of a resource required to service this request. Please review the following specific parse error details and modify your source file appropriately.

 Parser Error Message: Could not create type 'LookUp.LookUpService'.

Source Error:



Line 1:  <%@ WebService Language="C#" CodeBehind="LookUpService.asmx.cs" Class="LookUp.LookUpService" %>



 Source File:  /LookUp/LookUpService.asmx    Line:  1