PopUp Extender outside a repeater

Question

I have an ajax PopUpExtender outide a Repeter, it must be there becuase i use it Dynamicly on other contorls

i want the popup extender will be activated by Command of linkButton in the Repeater, I cant figure out how to add the TargetID to the popupID currectly here is my last shot:

    protected void lb_viewFileClick(object sender, CommandEventArgs e)
    {
        LinkButton lb = (LinkButton)sender;
        MDL_CD.TargetControlID = lb.ID;// I've also tried with ClientID
        MDL_CD.Show();
        HideControls();
        UC_ViewFile.Visible = true;
        PNL_CD.Visible = true;
    }

Answer 1

Figured it out!

 protected void rp_ProfileFils_ItemCommand(object source, RepeaterCommandEventArgs e)
 {
        int Index = e.Item.ItemIndex;
        LinkButton lb = (LinkButton)rp_ProfileFils.Items[Index].FindControl("hp_File");
        MDL_CD.TargetControlID = e.Item.UniqueID + "$hp_File";
 }