Hi I have a calender extender in a detailsview edititem template. how ever every time when i click update to finish the editing. there is always error says: the target control id of "calender extender 1 " is not valid. It works perfectly during the editing, has anybody got some idea?

Thanks in advance. 

<asp:TemplateField HeaderText="Start Date">

<ItemTemplate>

<asp:Label ID="LBLStartDate" runat="server" Text='<%# Eval("StartDate") %>'></asp:Label>

</ItemTemplate>

<EditItemTemplate>

<asp:TextBox ID="TxtStartdate" runat="server"></asp:TextBox>

<cc1:CalendarExtender ID="CalendarExtender1" runat="server" Enabled="True" TargetControlID='<%# DetailsView2.FindControl("TxtStartdate").ID %>' Format="dd/MM/yyyy" >

</cc1:CalendarExtender>

</EditItemTemplate>

</asp:TemplateField>

<EditItemTemplate>

<asp:TextBox ID="TxtStartdate" runat="server"></asp:TextBox>

<cc1:CalendarExtender ID="CalendarExtender1" runat="server" Enabled="True" TargetControlID="TxtStartdate" Format="dd/MM/yyyy" >

</cc1:CalendarExtender>

</EditItemTemplate>