how to copy one textbox value from another in javascript in asp.net gridview

I am trying to copy one text box to another textbox .I am getting error
like this  Cannot convert type 'system.web.ui.page' to 'system.web.ui.webcontrols.gridviewrow'

 
<script type="text/javascript">
    function OneTextToother()          
 {            
var first = document.getElementById('<%# ((GridViewRow)Container).FindControl("txtQuantity").ClientID %>');    
document.getElementById('<%# ((GridViewRow)Container).FindControl("txtQuantity1").ClientID %>').value=first;         }    
</script>
</head> <body>     <form id="form1" runat="server">     <div>    
<asp:GridView ID="gvOrder" runat="server" OnRowD ...