这是我的“购物车”的源代码：
<%@ Page Language="VB" Debug="true" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.OleDb" %>
<script runat="server">
     Dim Cpbt As DataTable
       Dim  Cpview as DataView
  Sub CrCpdatatable()
    Cpbt = New DataTable()
    Cpbt.Columns.Add(new DataColumn("CPID",GetType(String)))
    Cpbt.Columns.Add(new DataColumn("CPNAME",GetType(String)))
    Cpbt.Columns.Add(new DataColumn("CPDJ",GetType(single)))
    Cpbt.Columns.Add(new DataColumn("SL",GetType(Int32)))
    Cpbt.Columns.Add(new DataColumn("CPSUM",GetType(double)))
  End Sub
  Sub AddCpbt()
    Dim cpConn,Cpstring AS String
    Dim conn AS OleDbConnection
    Dim Cpadapter AS OleDbDataAdapter
    Dim Cpdat AS DataSet
    Dim dt AS DataTable
    cpConn = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & server.MapPath("data/dwdat.mdb")
    conn = New OledbConnection(cpConn)
    Cpstring = "SELECT CPID,CPNAME,CPDJ from DWCP WHERE CPID='" &Trim(Request.QueryString("CPID")) & "'"
    Cpadapter = new OleDbDataAdapter(Cpstring,conn)
    Cpdat = New DataSet()
    Cpadapter.Fill(Cpdat,"DWCP")
    dt = Cpdat.Tables("DWCP")
    Dim dr As DataRow = Cpbt.NewRow()
    dr(0) = dt.Rows(0)("CPID")
    dr(1) = dt.Rows(0)("CPNAME")
    dr(2) = dt.Rows(0)("CPDJ")
    dr(3) = 1
    dr(4) = dr(2) * dr(3)
    Cpbt.Rows.Add(dr)
     
  End Sub
  Sub CpTotal()
    Dim i As Integer
      Dim Cpto As single=0
      For i=0 to Cpbt.Rows.Count-1
         Cpto=Cpto+Cpbt.Rows(i)(4)
      Next
      CPCOUNT.text=Cpto
  End Sub
  Sub ByGrid_Delete(sender As Object, e As DataGridCommandEventArgs)

        Dim dr As DataRow = Cpbt.NewRow()
        Dim itemCell As TableCell = e.Item.Cells(0)
        Dim item As String = ItemCell.Text
         CpView.RowFilter = "CPID='" & item & "'"
            If  CpView.Count > 0 Then
                 CpView.Delete(0)
            End If
        CpView.RowFilter = ""
        CpTotal
          ByGrid.DataSource = CpView
        ByGrid.DataBind()
  End Sub
  Sub CpUpdate_Click(sender As object, e As EventArgs)
    Dim i,j As Integer
    Dim _item As DataGridItem
    j=0
    For i=0 To ByGrid.Items.Count-1
      _item = ByGrid.Items(i)
      Dim CountText As TextBox = _item.FindControl("Sltxt")
      Cpbt.Rows(i)(3) = CountText.Text
      Cpbt.Rows(i)(4) = Cpbt.Rows(i)(2) * Cpbt.Rows(i)(3)
    Next
          CpTotal
        ByGrid.DataSource = New DataView(Cpbt)
        ByGrid.DataBind()
  End Sub
  Sub ClearBy_Click(sender As object, e As EventArgs)
      Dim i As Integer
        For i=0 to CpView.Count-1
        CpView.Delete(0)
        Next
        CPCOUNT.text=0
        CpView.RowFilter = ""
      ByGrid.DataSource = CpView
      ByGrid.DataBind()
  End Sub
  Sub Page_Load(Sender As Object,e As EventArgs)
      If Session("Cpshop") Is Nothing Then
      CrCpdatatable
      Session("Cpshop") = Cpbt
    Else
      Cpbt = Session("Cpshop")
    End If
      Cpview = New DataView(Cpbt)
      If (Not IsPostBack) Then
        If Session("USERNAME")="" or Session("USERNAME")=nothing Then
         response.Redirect("nologin.htm")
        End If
        AddCpbt
            CpTotal
      ByGrid.DataSource = Cpview
      ByGrid.DataBind()
    End If
  End Sub
  Sub NewOrder_Click(sender As object, e As EventArgs)
    Dim cpConn,Cpstring AS String
    Dim conn AS OleDbConnection
    Dim Cpadapter AS new OleDbDataAdapter
    Dim Cpdat AS DataSet
    Dim dt AS DataTable
      Dim Newnow
      Dim Tystring as string
    cpConn = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & server.MapPath("dat/dwdat.mdb")
    conn = New OledbConnection(cpConn)
    Cpstring = "SELECT * from  CPDD"
       Cpadapter = new OleDbDataAdapter(Cpstring,conn)
      Dim yy as OleDbCommandBuilder=new OleDbCommandBuilder (Cpadapter)
      Cpdat = New DataSet()
    Cpadapter.Fill(Cpdat,"CPDD")
         DIM i as integer
      Newnow=now
      Tystring=session("USERNAME")+Cstr(year(Newnow))+iif(len(month(Newnow))=2,cstr(month(Newnow)),"0"+cstr(month(Newnow)))+iif(len(day(Newnow))=2,cstr(day(Newnow)),"0"+cstr(day(Newnow)))+cstr(hour(Newnow))+cstr(Minute(Newnow))+cstr(second(Newnow))
      For i=0 to Cpbt.Rows.Count-1
    Dim dr As DataRow =  Cpdat.Tables("CPDD").NewRow()
      dr(0) = Tystring
         dr(1) = Cpbt.Rows(i)("CPID")
      dr(2) = session("USERNAME")
         dr(3) = Cpbt.Rows(i)("SL")
    dr(4) = Newnow
    Cpdat.Tables("CPDD").Rows.Add(dr)
      next
      Cpadapter.Update(Cpdat, "CPDD")
      session("Cpshop")=nothing
      conn.close
      response.Redirect("ReEmail.aspx?DDID="+Tystring)
  End Sub
 
</script>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>无标题文档</title>
<style type="text/css">
<!--
.style1 {
      color: #FFFFFF;
      font-weight: bold;
      font-size: 12pt;
}
-->
</style></head>
<body >
  <div align="center">
    <form  runat="server">
  <table width="500"  border="0" cellpadding="2" cellspacing="0">
    <tr>
      <td height="30" bgcolor="#333333">
        <div align="left"><span class="style1">我的购物车</span></div></td>
    </tr>
    <tr>
      <td height="58" valign="top"> <ASP:DataGrid AllowPaging="false"
       AutoGenerateColumns="false"
       BackColor="white"
       BorderColor="black"
       CellPadding=3
       CellSpacing="0"
       Font-Name="Verdana"
       Font-Size="8pt"
       HeaderStyle-BackColor="#aaaadd" id="ByGrid" runat="server"
       ShowFooter="false"
       Width="90%" OnDeleteCommand="ByGrid_Delete"
       MaintainState="false">
     <Columns>
       <asp:BoundColumn DataField="CPID" HeaderText="产品品编号" />
       <asp:BoundColumn DataField="CPNAME" HeaderText="产品名" />
       <asp:BoundColumn DataField="CPDJ" HeaderText="单价" DataFormatString="{0:c}"/>
       <asp:TemplateColumn HeaderText="数量">
         <ItemTemplate>
             <asp:TextBox id="Sltxt" width="50" runat="server" Text='<%#Container.DataItem("SL")%>' />
           </ItemTemplate>
       </asp:TemplateColumn>
         <asp:BoundColumn DataField="CPSUM" HeaderText="小计(元)" DataFormatString="{0:c}"/>
         <asp:ButtonColumn
        ButtonType="LinkButton"
        CommandName="Delete"
        HeaderText="删除"
        Text="删除"
        Visible="True"/>    
     </Columns>
  </asp:DataGrid>
       </td>
    </tr>
    <tr>
      <td height="19" valign="top" align="left" style="font-size:9pt "><strong>合计：
          <asp:Label ID="CPCOUNT" runat="server" />                   
        </strong></td>
    </tr>
    <tr >
      <td height="23" bgcolor="#F7F7F7"><div align="center">
        <p>
          <asp:Button ID="SxBt" runat="server" Text="刷新购物车" OnClick="CpUpdate_Click" />         
&nbsp;
<asp:Button ID="ClBt" runat="server" Text="清空购物车" OnClick="ClearBy_Click" />
&nbsp;
<asp:Button ID="NewOrder" runat="server" Text="确定下订单" OnClick="NewOrder_Click" />
&nbsp;
<input name="ExBt" type="button" id="ExBt" value="退出购物车" OnClick=window.close()">
</p>
        </div></td>
    </tr>
  </table>

 
       
    </form></div>
</body>
</html>

提示：
Exception Details: System.Data.OleDb.OleDbException: Data type mismatch in criteria expression.

Source Error:

Line 24:     Cpadapter = new OleDbDataAdapter(Cpstring,conn)
Line 25:     Cpdat = New DataSet()
Line 26:     Cpadapter.Fill(Cpdat,"DWCP")
Line 27:     dt = Cpdat.Tables("DWCP")
Line 28:     Dim dr As DataRow = Cpbt.NewRow()