<td> <asp:TextBox ID="txtDate" runat="server" ReadOnly="true"></asp:TextBox> </td> <td> <asp:ImageButton ID="imgCalender" runat="server" ImageUrl="~/Images/Calendar.png" ToolTip="Select a Date" /> <asp:CalendarExtender ID="calShow" runat="server" PopupButtonID="imgCalender" PopupPosition="BottomLeft" TargetControlID="txtDate" OnClientDateSelectionChanged="CheckForPastDate"></asp:CalendarExtender> </td>