Help me with this error

<html>  
      <head>  
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />  
         <meta http-equiv="Pragma" content="no-cache" />  
       <meta http-equiv="Expires" content="-1" />  
      <meta http-equiv="Cache-Control" content="no-cache" />  
      <title>Sigma Grid Tutorial 1</title>  
      <link rel="stylesheet" type="text/css" href="grid/gt_grid.css" />  
      <script type="text/javascript" src="grid/gt_msg_en.js"></script>
      <script type="text/javascript" src="grid/gt_const.js"></script>
      <script type="text/javascript" src="grid/gt_grid_all.js"></script>
            <script type="text/javascript" >  
       
      var data1 = [
          {serialNo:"010-0",country:"MA",employee:"Jerry",customer:"Keith",order2005:50,order2006:57,order2007:80,order2008:46,lastDate:"2008-10-02"},
       {serialNo:"010-1",country:"SP",employee:"Charles",customer:"Marks",order2005:79,order2006:37,order2007:40,order2008:90,lastDate:"2008-04-24"},
      {serialNo:"010-2",country:"SP",employee:"Vincent",customer:"Harrison",order2005:91,order2006:75,order2007:31,order2008:40,lastDate:"2008-02-17"},
      {serialNo:"020-3",country:"RA",employee:"Edward",customer:"Sidney",order2005:61,order2006:31,order2007:80,order2008:47,lastDate:"2008-10-16"}
      ];
      
         var dsOption= {
       			   fields :[
           		  {name : "serialNo"},
            	  {name : "country"},
                 {name : "customer"  },
                 {name : "employee"},
                {name : 'order2005' ,type: 'float' },
                {name : 'order2006' ,type: 'float' },
                {name : 'order2007' ,type: 'float' },
                 {name : 'order2008' ,type: 'float' },
                 {name : 'lastDate' ,type:'date'  }    
           ],
            recordType : 'object',
          data: data1
      }

var colsOption = [

{id: 'serialNo' , header: "Order No" , width :60 },

{id: 'employee' , header: "Employee" , width :80  },

{id: 'country' , header: "Country" , width :70  },

{id: 'customer' , header: "Customer" , width :80  },
 
             {id: 'order2005' , header: "2005" , width :60},

{id: 'order2006' , header: "2006" , width :60},

{id: 'order2007' , header: "2007" , width :60},

{id: 'order2008' , header: "2008" , width :60},

{id: 'lastDate' , header: "Delivery Date" , width :100}

];
     
       var gridOption={
          id : "grid1",
          container : 'grid1_container', 
          dataset : dsOption ,
          columns : colsOption
      };
     var mygrid=new Sigma.Grid(gridOption);
      Sigma.Util.onLoad( Sigma.Grid.render(mygrid) );
      </script>  
     </head>  
      <body>  
       <div id="grid1_container" style="width:700px;height:300px">   </div>  
     </body>  
      </html>

When i load the page , a popup show up with content:"LOAD ERR , XMLHttpRequest Status : url is null".
Please help me, i'm new sigmagrid.
Thanks.