Use This ConfirmButtonExtebder :)
<itemtemplate>
<asp:linkbutton id="LinkButton1" runat="server" causesvalidation="False" commandname="Delete" xmlns:asp="#unknown">
Text="Delete"></asp:linkbutton><cc1:confirmbuttonextender id="LinkButton1_ConfirmButtonExtender" xmlns:cc1="#unknown">
runat="server" ConfirmText="Are you sure you want to delete?" Enabled="True"
TargetControlID="LinkButton1">
</cc1:confirmbuttonextender>
pre lang="c#"></itemtemplate>
e>