is that something wrong in the below code? its not firing at all

$(document).ready(function() {    
          $("#<%=txtHost.ClientID%>").autocomplete("HostService.asmx/GetHosts",{    
            dataType: 'json'    
            ,contentType: "application/json; charset=utf-8"    
            ,parse: function(data){    
                var rows = Array();  
                debugger   
                for(var i = 0; i<data.length; i++){    
                    rows[i] = {data:data[i], value:data[i].LName, result:data[i].LName};    
                }    
                return rows;    
            }    
            ,formatItem: function(row, i, max){    
                return data.LName + ", " + data.FName;    
            }    
        });  
      });  

           <script src="Scripts/jquery.autocomplete.js" type="text/javascript"></script> 

        <asp:TextBox ID="txtHost" runat='server'></asp:TextBox>