Could not display Class breaks render.

I am developing a Windows Application by using VB.net and ArcGIS Engine 9.1. I followed the sample code from EnginDevGD document to make a window form that covers AxMapControl, AxTOCControl, and AxToolbarControl, and loaded a .mxd file in VB.net code. It ran fine. Then I tried to create a button for generating a class breaks render for one layer that existing in the .mxd file. The layer is a polygon shape file with single symbol and I would like to render it to 4 classes and show them as circle graduated symbols. I searched most of the code that I can find on internet and rewrote them to achieve this goal. When I clicked the "render" button, I didn't see any error message. However, neither AxTOCControl nor AxMapControl displayed any render symbol. I think something must be wrong in my vb.net code. Could anyone please check my code attached below? Thanks in advance.
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Private Sub btnRender_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnRender.Click

Dim pMap As IMap
pMap = AxMapControl1.Map
Dim pLayer As ILayer
Dim i As Integer
For i = 0 To pMap.LayerCount - 1
    pLayer = pMap.Layer(i)
    If pLayer.Name = "Produc" Then    '<---the layer that is desired to be rendered
          pLayer = pMap.Layer(i)
       Dim pFlayer As IFeatureLayer
       pFlayer = pLayer
       Dim pLyr As IGeoFeatureLayer
       pLyr = pFlayer

                
 'create a render and classify the data
       Dim pCBR As IClassBreaksRenderer
       pCBR = New ClassBreaksRenderer

       Dim ValRange As Double = 0
       ValRange = MaxVal - MinVal

       Dim strLegendHeading As String = ""

       With pCBR
            .BreakCount = 4

            If MaxVal > 100000 And MaxVal < 100000000 Then
               .Break(0) = CInt(MinVal / 1000)
               .Break(1) = CInt((MinVal + (ValRange / 4)) / 1000)
               .Break(2) = CInt((MinVal + (ValRange / 2)) / 1000)
               .Break(3) = CInt(MaxVal / 1000)
                        
               strLegendHeading = "Tons in Thousands"
             ElseIf MaxVal > 100000000 Then
               .Break(0) = CInt(MinVal / 1000000)
               .Break(1) = CInt((MinVal + (ValRange / 4)) / 1000000)
               .Break(2) = CInt((MinVal + (ValRange / 2)) / 1000000)
               .Break(3) = CInt(MaxVal / 1000000)
                strLegendHeading = "Tons in Millions"
            Else
                .Break(0) = CInt(MinVal)
                .Break(1) = CInt(MinVal + (ValRange / 4))
                .Break(2) = CInt(MinVal + (ValRange / 2))
                .Break(3) = CInt(MaxVal)
                        strLegendHeading = "Tons"
                    End If

                .Field = "SumOfValue"
      End With

      Dim pColor As IRgbColor
      pColor = New RgbColor
      pColor.RGB = RGB(255, 0, 0)

                
      Dim pMarkerSym As ISimpleMarkerSymbol
      pMarkerSym = New SimpleMarkerSymbol

      Dim pSym As ISymbol
      Dim j As Integer

'Generate graduated symbols
      For j = 0 To 3
          pMarkerSym.Size = (12 + (5 * j))
          pMarkerSym.Color = pColor
          pMarkerSym.Style = esriSimpleMarkerStyle.esriSMSCircle
          pSym = pMarkerSym
          pCBR.Symbol(j) = pSym
      Next j

      pLyr.Renderer = pCBR

      'Establish a heading for legend in the TOCControl
      Dim pLegendInfo As ILegendInfo
      pLegendInfo = pCBR
      pLegendInfo.LegendGroup(0).Heading = strLegendHeading

      'redraw the TOC and the map
      AxTOCControl1.Update()
      AxMapControl1.ActiveView.Refresh()
      Exit For
   Else

      End If
   Next i
End Sub
*********************************************************************

你好,are you 老外?   <img src="images/post/smile/dvbbs/em03.gif" /><img src="images/post/smile/dvbbs/em03.gif" />

<P>很抱歉,因為沒有中文鍵盤,所以直接轉貼我在 ESRI Support Center 所提出的問題,我希望能在這邊得到一些指點。</P>
<P>終於借到鍵盤了,讓我重新把問題描述一便。</P>
<P>小弟正在用VB.NET 及 AE9.1 撰寫一個 WINDOWS 的應用程式。我依照 EnginDevGD 文件裏的範例程式碼來創建一個有AxMapControl, AxTOCControl, and AxToolbarControl 的 window form ,並在程式運行當中加載一個 .mxd 檔顯現在AxMapControl。整個程式運作正常。接著我試著創建一個按扭,當我按下它時可對某個已存在 .MXD 檔的 LAYER 生成 class breaks render, (該 LAYER 原始設定是The single symbol 的 POLYGON Shapefile)。 我希望能對該layer生成4個classes並用四個不同大小的圓形符號表示 (就像在ArcMap 中對layer的Symbology屬性設定為用Quantities的Graduted symbols方法來表示)。 我是參照我所能在網路上找到的程式碼並修改它们來實現這個目地l。 當我按下 "render" 鈕時,程式運行完畢,且沒有出現任何錯誤訊息。 然而, 在 AxTOCControl 及 AxMapControl 並未顯示我要的 render symbol。 我想我的vb.net 程式碼必定在那裏出錯了。 有那位大俠可簡查我的程式碼 (貼在樓上) ? 先謝謝了 !!!<BR></P>