Error: Collection was modified; enumeration operation may not execute.

Hi There,

I'm getting an error when I try to update multiple rows from shopping cart. When I have one row it works fine but when I have multiple rows it gives me the error "Collection was modified; enumeration operation may not execute. " after the first iteration of the loop.

Could someone help me out with the syntax please?

Sean

!--- code

 Sub ChangeQuantity(ByVal send As Object, ByVal E As EventArgs)
        Dim i As Int32 = 0
        Dim strCode As String = ""
        Dim intusercode As Int32 = 0
        ' For i = 0 To cart.Items.Count - 1
        For Each dataItem As RepeaterItem In cart.Items
            Dim ItemQuantity As TextBox = (CType(dataItem.FindControl("ItemQuantity"), TextBox))
            Dim txtcode As TextBox = (CType(dataItem.FindControl("txtcode"), TextBox))
            Dim txtitemnumber As Label = (CType(dataItem.FindControl("lblPitemnumber"), Label))
            Dim lblprice As Label = (CType(dataItem.FindControl("lblprice"), Label))
            If Not txtcode.Text = "" Then
                strCode = GetValidCode(txtcode)
                If strCode Is Nothing Then 'if the user does not have a valid code then call the function
                    Call UpdateCart(ItemQuantity, txtcode, txtitemnumber, lblprice, intusercode)
                Else 'if the user has a valid code then look it up
                    Session("THECODE") = strCode
                    intusercode = 1
                    Call GetDistributorPrice(ItemQuantity, txtcode, txtitemnumber, lblprice, intusercode)
                End If
            Else
                'if the code is nothing then call the function
                Call UpdateCart(ItemQuantity, txtcode, txtitemnumber, lblprice, intusercode)
            End If
            'Exit For
        Next
    End Sub


!--- repeater code

<asp:repeater id="cart" runat="server">
                        <HeaderTemplate>
                              <table border="1" cellpadding="3" style="background-color:#F6F6F6; border-collapse:collapse">
                                    <tr>
                                          <th>
                                                Number</th>
                                          <th>
                                                Title</th>
                                          <th>
                                                Price</th>
                                          <th>
                                                Quantity</th>
                                          <th>
                                                MTA / Reseller Code</th>
                                          <th>
                                                Amount</th>
                                          <th>
                                                &nbsp;
                                          </th>
                                    </tr>
                        </HeaderTemplate>
                        <ItemTemplate>
                              <tr>
                                    <td align="center">Item Number:
                                          <%# Container.DataItem("Pitemnumber") %>
                                          <asp:Label id="lblPitemnumber" runat="server" ReadOnly="True" Visible="false" Text='<%# Container.DataItem("Pitemnumber") %>'>
                                          </asp:Label>
                                    </td>
                                    <td align="left">Item Name:
                                          <asp:Label id="lblPitemname" runat="server" ReadOnly="True" Visible="true" Text='<%# Container.DataItem("Pname") %>'>
                                          </asp:Label>
                                    </td>
                                    <td align="right">Item Price:
                                          <asp:Label id="lblprice" runat="server" ReadOnly="True" Visible="true" Text='<%# Container.DataItem("Pprice") %>'>
                                          </asp:Label>
                                          <asp:Label id="lblPhandling" runat="server" ReadOnly="True" Visible="False" Text='<%# Container.DataItem("Phandling") %>'>
                                          </asp:Label>
                                    </td>
                                    <td align="center">
                                          <asp:TextBox id="ItemQuantity" runat="server" Text='<%# Container.DataItem("Pitemquantity") %>' MaxLength="2" Style="width:30px; text-align:right"/>
                                    </td>
                                    <td>
                                          <asp:TextBox id="txtcode" runat="server" MaxLength="11" Style="width:100px; text-align:right" /></td>
                                    <td align="right"><b><%# FormatNumber(GetItemAmount(Container.DataItem("Pprice"), Container.DataItem("pitemquantity")), 2) %></b></td>
                        </ItemTemplate>
                        <FooterTemplate>
                              <tr>
                                    <th align="right" colspan="4">
                                          Postage & Handling:
                                    </th>
                                    <td align="right"><b><%# FormatCurrency(GetOrderShipping()) %></b></td>
                              </tr>
                              <tr>
                                    <th align="right" colspan="4">
                                          Order Total:
                                    </th>
                                    <td align="right"><b><%# FormatCurrency(GetOrderTotal()) %></b></td>
                                    <td>
                                          <asp:Button Text="Update" class="small" runat="server" onclick="ChangeQuantity" ID="Button1"
                                                NAME="Button2" />
                                    </td>
                              </tr>
                        </FooterTemplate>
                  </asp:repeater>