Solved
adding a Table structure
<asp:UpdatePanel ID="UpdatePanel2" runat="server" Visible="true">
<ContentTemplate>
<asp:Panel ID="pnlDia1" runat="server">
<asp:Table ID="Table1" runat="server">
<asp:TableRow>
<asp:TableCell>
.............
</asp:TableCell>
</asp:TableRow>
</asp:Table>
</asp:Panel>
</ContentTemplate>
</asp:UpdatePanel>