Opening RadWindow for Formview Control

[jai]

Hi

How to open radwindow from onclick button in FormView Control

<

telerik:RadWindowManager id="Singleton" runat="server" ClientCallBackFunction="CallBackFunction">
<windows>
<telerik:RadWindow id="DialogWindow"
OpenerElementId = "<%# Button1.ClientID %>" Left="250px"Modal = "true"Runat="server" Width="270px" Height="200px" Title="User List Dialog" NavigateUrl="~/Pages/Lookup.aspx">
</telerik:RadWindow></windows>
</telerik:RadWindowManager>

<

asp:FormView ID="formView" runat="server">
<EditItemTemplate>

<

asp:Button ID="Button1" runat="server" Text="Button" />

</EditItemTemplate></asp:FormView >

Getting error that 'Button1.ClientID' cannot not find...
Please guide to fix the issue..

Regards
Jai