using System;
using System.Web;
using System.Collections;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Data;
using System.Web.Configuration;


[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.Web.Script.Services.ScriptService]
public class WebService : System.Web.Services.WebService {    

    [WebMethod()]
    public List<TerritoriesService> GetTerritory(int ID)
    {
          ......
    }
}

The type or namespace name 'Script' does not exist in the namespace 'System.Web' (are you missing an assembly reference?)