GridView not able to enter edit mode

Hi all,

  My gridview is setup as follow :

  <asp:UpdatePanel ID="updatePanel" runat="server" UpdateMode="Conditional">
            <ContentTemplate>    
            <asp:GridView style="position:absolute; left:200px; top: 400px; width: 485px; height: 29px;" 
            ID="gvCase" runat=server Visible="False" AllowPaging="True" BackColor="White"
            BorderColor="#999999" BorderStyle="None" BorderWidth="1px" CellPadding="3"
            Font-Names="verdana" Font-Size="XX-Sma ...