here my code,did i make any mistake...
<asp:Button ID="btnassign" runat="server" Text="Assign"
onclick="btnassign_Click" />
<asp:Panel ID="option" runat="server" >
<asp:DropDownList ID="ddlnwkeng" runat="server" AutoPostBack="True">
<asp:ListItem>--select--</asp:ListItem>
<asp:ListItem>Abdul</asp:ListItem>
</asp:DropDownList>
</asp:Panel>
<asp:ModalPopupExtender ID="ModalPopupnwkeng" DropShadow="true" TargetControlID="btnassign" PopupControlID="option" runat="server">
</asp:ModalPopupExtender>