I'm getting this error in IE6 on some machines using CollapsiblePanelExtender

The collpsiblePane is inside a repeater control (code below)
 

      <h2><asp:Label ID="LblUf" runat="server" Text=""></asp:Label><br /></h2>
      <asp:Literal ID="Literal1" runat="server" Text='"font-size:11px;">Clique na cidade para ver os endereços!</span>' Visible="false"></asp:Literal>
      <span style="font-size:11px;">Clique na cidade para ver os endereços!</span>
      <asp:DataList ID="DataList1" runat="server" DataSourceID="DsUnidades">
        <ItemTemplate>
            <cc1:CollapsiblePanelExtender ID="CollapsiblePanelExtender1" runat="server" 
                TargetControlID="Panel1"
                ExpandControlID="HyperLink1"
                CollapseControlID="HyperLink1"
                AutoCollapse="False"
                AutoExpand="False"
                ScrollContents="False"
                ExpandDirection="Vertical"
                Collapsed="True">
            </cc1:CollapsiblePanelExtender>
            <div class="accHeaderGray" style="width:500px"><asp:HyperLink ID="HyperLink1" runat="server" NavigateUrl="javascript:void(0);"><%#Eval("CID_UNIDADE") %></asp:HyperLink></div>
            <asp:Panel ID="Panel1" runat="server" Height="0px">
                <div class="accContent" style="width:500px">
                    <asp:Repeater ID="Repeater2" runat="server">
                        <ItemTemplate>
                            <strong><%#Eval("NOM_UNIDADE") %></strong><br />
                            <%#Eval("END_UNIDADE") %><br />
                            Telefone(s): <%#Eval("FONE1_UNIDADE") %> | <%#Eval("FONE2_UNIDADE") %><br />                            
                        </ItemTemplate>
                        <SeparatorTemplate>
                            <div style="margin-bottom:10px;padding-bottom:5px;border-bottom:1px solid #ccc;"></div>
                        </SeparatorTemplate>
                    </asp:Repeater>                
                </div>
            </asp:Panel>                         
        </ItemTemplate>
      </asp:DataList>
      <asp:SqlDataSource ID="DsUnidades" runat="server" ConnectionString="<%$ ConnectionStrings:ConnString %>"
          SelectCommand="SELECT COUNT(COD_UNIDADE) AS CONTADOR, CID_UNIDADE

FROM         UNIDADE

WHERE     (UF_UNIDADE = @UF)

GROUP BY CID_UNIDADE

ORDER BY CID_UNIDADE">
          <SelectParameters>
              <asp:QueryStringParameter DefaultValue="nn" Name="UF" QueryStringField="UF" />
          </SelectParameters>
      </asp:SqlDataSource>

I do some manipulate in code behind:

    Protected Sub DataList1_ItemDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.DataListItemEventArgs) Handles DataList1.ItemDataBound
        Dim Item As DataListItem = e.Item
        If Item.ItemType = ListItemType.Item Or e.Item.ItemType = ListItemType.AlternatingItem Then
            Dim Cidade As String = e.Item.DataItem("CID_UNIDADE")

            Dim Panel1 As Panel = DirectCast(e.Item.FindControl("Panel1"), Panel)
            Dim Repeater2 As Repeater = DirectCast(Panel1.FindControl("Repeater2"), Repeater)

            Dim UnidadeTAdapter As New DALTableAdapters.UNIDADETableAdapter
            Dim UnidadeTable As DAL.UNIDADEDataTable = UnidadeTAdapter.GetUnidadesPorCidade(Cidade)
            Repeater2.DataSource = UnidadeTable
            Repeater2.DataBind()
            UnidadeTable = Nothing
            UnidadeTAdapter = Nothing
        End If
    End Sub

The more strange on all this is when I go in the client to see the problem "in loco" (everything is fine on my development machines IE and Firefox).

When I installed the .net 1.1 to make fiddler works to see if there is any problem in the load scripts the problem has been solved on those machines.

I've used the collapsiblepane in other areas of the site and only in this especific page this is happening.

You can see it real time on (in portuguese but very easy - just click on a brasil state - more dark ones - to see a list of towns - click on name of town to see the collapsiblepane):

http://www.uptimesite.com.br/estudar/Default.aspx

Thanks for any reply. 

 John