Maintaining state of a control in a repeater in asp.net

Question

I'm having a bit of an issue trying to get a control in a repeater to maintain state.

I have a custom control (KPIbtn) which is basically a 4 position toggle, that I need to keep value between postbacks.

The value is based on a datatable.

To get this interface up and running I have the KPIbtn created dynamically in a placeholder in a repeater.

This all works fine until I add a another field (StuName) to the repeater. with the extra field on postback I get an error:

Multiple controls with the same ID 'StuName' were found. FindControl requires that controls have unique IDs.

Remove the field - no problems, have the field, but no dynamic control creation, no problems. both - the error appears.

The repeater section of the page looks like...

  <asp:Repeater ID="Repeater1" runat="server"  OnItemCreated="Repeater1_ItemCreated" OnItemDataBound="Repeater1_ItemDataBound">
                <ItemTemplate>
         <div>
             <asp:Label ID="StuName" runat="server" Text='<%#Eval("StuID") %>'></asp:Label>
               <asp:PlaceHolder ID="PlaceHolder2" runat="server"></asp:PlaceHolder>
         </div>
     </ItemTemplate>
        </asp:Repeater> 

and the code behind is

protected void Repeater1_ItemCreated(object sender, RepeaterItemEventArgs e)
{
        if (Page.IsPostBack)
        {
            DTable = ViewState["DTable"] as DataTable;
        }

        foreach (DataColumn dc in DTable.Columns)
        {
            KPIbtn btn = new KPIbtn();
            btn.ID = dc.ColumnName;
            btn.KPIID = dc.ColumnName;
            btn.StuID = "test";

            PlaceHolder rep = e.Item.FindControl("PlaceHolder2") as PlaceHolder;
            rep.Controls.Add(btn);
        }
}

Any thoughts on what I am missing or doing wrong? The easy option looks like finding another way of referring to the placeholder without using 'find control', but I fear that at the best that would be glossing over an underlying problems, and there is probably no other option anyway.