Still doesn't work. I'm doing standard editing now and it still reverts back to the old value, even for the textbox (Quantity) field. I'm goihg to post my whole source code in hope that some superhero will fly down and save me (Your cue, Imar).

<%@ Page Language="VB" MasterPageFile="~/MerchDB.master" AutoEventWireup="false" CodeFile="ConferenceStore.aspx.vb" Inherits="ConferenceStore" title="SCGIS - Store" %>

<%@ Register Assembly="AtlasControlToolkit" Namespace="AtlasControlToolkit" TagPrefix="cc1" %>
<%@ MasterType VirtualPath="~/MerchDB.master" %>

<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<div style="font-family: Verdana, Sans-Serif;">
<atlas:ScriptManager ID="sm" runat="server" EnablePartialRendering="true"></atlas:ScriptManager>
    <table>
        <tr>
            <td width=540 valign="top">
               <atlas:UpdatePanel ID="UP1" Mode="Conditional" runat="server">
                <ContentTemplate>
                    <asp:GridView DataKeyNames="pkProductID" ID="gvMerchandise" runat="server" AlternatingRowStyle-BackColor="Beige" GridLines="Horizontal" AllowSorting="True" AutoGenerateColumns="False" DataSourceID="ObjectDataSource2" Width="540px" BackColor="White" BorderColor="#336666" BorderStyle="Double" BorderWidth="3px" CellPadding="4" EditRowStyle-Width="100px" EmptyDataRowStyle-Width="100px" PageSize="6" Font-Size="8pt">
                        <Columns>
                            <asp:BoundField DataField="ProductName" HeaderText="ProductName" SortExpression="ProductName" ItemStyle-Width="100"/>
                            <asp:BoundField DataField="Description" HeaderText="Description" SortExpression="Description" ItemStyle-Width="160" />
                            <asp:BoundField DataField="Price" DataFormatString="{0:C}" HtmlEncode="false" HeaderText="Price" SortExpression="Price" ItemStyle-Width="60"/>
                            <asp:ImageField DataImageUrlField="ImageName">
                                <ControlStyle Width="80px" />
                                <ItemStyle Width="80px" />
                            </asp:ImageField>
                            <asp:ButtonField CommandName="AddToCart" Text="Add to Cart" ItemStyle-Width="80" />
                        </Columns>
                        <FooterStyle BackColor="White" ForeColor="#333333" />
                        <RowStyle BackColor="White" ForeColor="#333333" />
                        <SelectedRowStyle BackColor="#339966" Font-Bold="True" ForeColor="White" />
                        <PagerStyle BackColor="#336666" ForeColor="White" HorizontalAlign="Center" />
                        <HeaderStyle BackColor="#203738" Font-Bold="True" ForeColor="White" />
                        <AlternatingRowStyle BackColor="Beige" />
                        <EmptyDataRowStyle Width="100px" />
                        <EditRowStyle Width="100px" />
                    </asp:GridView>
                </ContentTemplate>

                </atlas:UpdatePanel>


            </td>
            <td valign=top width=200>

                <cc1:AlwaysVisibleCont********************tender ID="AlwaysVisibleCont********************tender1" runat="server">
                <cc1:AlwaysVisibleControlProperties TargetControlID="divCart" HorizontalSide="Left" HorizontalOffset="680" VerticalOffset="10" ScrollEffectDuration=".1" />
                </cc1:AlwaysVisibleCont********************tender>
                <div ID="divCart" runat="server" style="Position:absolute; top: 10px; border: 1px black solid; width: 360px; left: 680px; background-color: GhostWhite;">
                    <div style="margin-top: 0px; font-size: 10pt; font-weight:bold; " align="center">Shopping Cart</div>
                    <atlas:UpdatePanel ID="UP3" runat="server" Mode="Conditional">
                        <ContentTemplate>
                            <asp:GridView ID="gvCart" DataKeyNames="pkCartItemID" runat="server" AutoGenerateColumns="False" Width="360px" AlternatingRowStyle-BackColor="Cornsilk" HeaderStyle-BackColor="#203738" HeaderStyle-ForeColor="White">
                                <Columns>

                                    <asp:CommandField ShowDeleteButton="True" ShowEditButton="True" />
                                    <asp:BoundField DataField="ProductName" HeaderText="Item Name" ReadOnly = "True" />
                                    <asp:TemplateField HeaderText="Size">
                                        <EditItemTemplate>
                                            <asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("Size") %>'></asp:TextBox>
                                        </EditItemTemplate>
                                        <ItemTemplate>
                                            <asp:Label ID="Label1" runat="server" Text='<%# Bind("Size") %>'></asp:Label>
                                        </ItemTemplate>
                                        <ControlStyle Width="80px" />
                                    </asp:TemplateField>
                                    <asp:BoundField DataField="UnitPrice" ReadOnly="True" HeaderText="Price" DataFormatString="{0:C}" HtmlEncode="False"/>
                                    <asp:TemplateField HeaderText="Qty.">
                                        <EditItemTemplate>
                                            <asp:TextBox ID="tbQty" runat="server" Text='<%# Bind("Quantity") %>'></asp:TextBox>
                                        </EditItemTemplate>
                                        <ControlStyle Width="30px" />
                                        <ItemStyle HorizontalAlign="Center" />
                                        <ItemTemplate>
                                            <asp:Label ID="Label2" runat="server" Text='<%# Bind("Quantity") %>'></asp:Label>
                                        </ItemTemplate>
                                    </asp:TemplateField>
                                    <asp:BoundField DataField="ExtendedPrice" ReadOnly="True" HeaderText="Ext. Price" DataFormatString="{0:C}" HtmlEncode="False" />
                                    <asp:CheckBoxField DataField="booPerk" HeaderText="Free Perk?" />

                                </Columns>
                                <RowStyle Font-Size="8pt" />
                                <HeaderStyle Font-Names="verdana,sans-serif" Font-Size="8pt" BackColor="#203738" ForeColor="White" />
                                <AlternatingRowStyle BackColor="Cornsilk" />
                            </asp:GridView>

                            <div align="center">
                                <asp:Label ID="lblCartEmpty" runat="server" Visible=False Font-Bold="true" Font-Size="8"><br>Empty<br></asp:Label>
                            </div>
                            <div id="divButtons" runat="server" style="visibility: hidden;">
                                <table width="360">
                                    <tr>
                                        <td align="left">
                                            <asp:Button id="btnEmptyCart" runat="server" Text="Empty Cart" />
                                        </td>
                                        <td align="right">
                                            <asp:Button id="btnCheckout" runat="server" Text="Checkout" />
                                        </td>
                                    </tr>
                                </table>
                            </div>


                        </ContentTemplate>
                        <Triggers>
                            <atlas:ControlEventTrigger ControlID="gvMerchandise" EventName="RowCommand" />
                        </Triggers>
                    </atlas:UpdatePanel>

                </div>
            </td>
        </tr>
    </table>

        <asp:ObjectDataSource ID="ObjectDataSource2" runat="server" OldValuesParameterFormatString="original_{0}" SelectMethod="GetData"
        TypeName="dsMerch2TableAdapters.tbl_SCGISMerchandi seTableAdapter">
    </asp:ObjectDataSource>



</div>
</asp:Content>



Codebehind now

Imports System.Data
Imports System.Data.SqlClient

Partial Class ConferenceStore
    Inherits System.Web.UI.Page

    Dim dsItemsOrdered As New DataSet

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not IsPostBack Then
            'Session("dssItemsOrdered") = Nothing
            'Session("dsItemsOrdered") = Nothing
            'Session("Invoice") = Nothing
            'Session("GrandTotal") = Nothing
            'Session("CartDetailsHTML") = Nothing
            'Session("CartDetailsText") = Nothing

        End If

        If Not Session("MerchLoggedIn") = True Then
            'Response.Redirect("MerchLogin.aspx?ReturnPath=Mer chDatabase.aspx")
        End If

        'Create OrderItem dataset if it doesn't exist already
        'if it does exist, load from Session

        If Session("dssItemsOrdered") Is Nothing Then

            dsItemsOrdered.Tables.Add("ItemsOrdered")
            dsItemsOrdered.Tables("ItemsOrdered").Columns.Add( "pkCartItemID", System.Type.GetType("System.Int16"))
            dsItemsOrdered.Tables("ItemsOrdered").Columns(0).A utoIncrement = True
            dsItemsOrdered.Tables("ItemsOrdered").Columns(0).A utoIncrementSeed = 1
            dsItemsOrdered.Tables("ItemsOrdered").Columns(0).A utoIncrementStep = 1

            dsItemsOrdered.Tables("ItemsOrdered").Columns.Add( "ProductID", System.Type.GetType("System.Int16"))
            dsItemsOrdered.Tables("ItemsOrdered").Columns.Add( "ProductName", System.Type.GetType("System.String"))
            dsItemsOrdered.Tables("ItemsOrdered").Columns.Add( "Size", System.Type.GetType("System.String"))
            dsItemsOrdered.Tables("ItemsOrdered").Columns.Add( "UnitPrice", System.Type.GetType("System.Single"))
            dsItemsOrdered.Tables("ItemsOrdered").Columns.Add( "Quantity", System.Type.GetType("System.Int16"))
            dsItemsOrdered.Tables("ItemsOrdered").Columns.Add( "ExtendedPrice", System.Type.GetType("System.Single"))
            dsItemsOrdered.Tables("ItemsOrdered").Columns.Add( "booPerk", System.Type.GetType("System.Boolean"))



            'Store dataset in session
            Dim stream As New System.IO.StringWriter
            dsItemsOrdered.WriteXml(stream, XmlWriteMode.DiffGram)
            Session("dsItemsOrdered") = stream
            Session("dssItemsOrdered") = dsItemsOrdered.GetXmlSchema
        Else

            'get xml back from Session
            Dim sr As New System.IO.StringReader(Session("dsItemsOrdered").T oString)
            Dim srr As New System.IO.StringReader(Session("dssItemsOrdered"))
            dsItemsOrdered.ReadXmlSchema(srr)
            dsItemsOrdered.ReadXml(sr)

        End If

        Me.gvCart.DataSource = dsItemsOrdered
        Me.gvCart.DataMember = "ItemsOrdered"
        Me.gvCart.DataBind()

        If dsItemsOrdered.Tables(0).Rows.Count <= 0 Then
            Me.lblCartEmpty.Visible = True
            divButtons.Style.Item("visibility") = "hidden"
        Else
            Me.lblCartEmpty.Visible = False
            divButtons.Style.Item("visibility") = "visible"
        End If
    End Sub

    Protected Sub gvCart_Editing(ByVal sender As Object, ByVal e As GridViewEditEventArgs) Handles gvCart.RowEditing
        gvCart.EditIndex = e.NewEditIndex
        DataBind()
    End Sub

    Protected Sub gvCartEditing_Canceling(ByVal sender As Object, ByVal e As GridViewCancelEditEventArgs) Handles gvCart.RowCancelingEdit
        gvCart.EditIndex = -1
        DataBind()
    End Sub

    Protected Sub gvCart_Updating(ByVal sender As Object, ByVal e As GridViewUpdateEventArgs) Handles gvCart.RowUpdating
        Dim row As GridViewRow = gvCart.Rows(e.RowIndex)
        If Not row Is Nothing Then
            Dim tb As TextBox = CType(row.FindControl("tbQty"), TextBox)
            Dim dr As DataRow = dsItemsOrdered.Tables(0).Rows(e.RowIndex)
            dr("Quantity") = tb.Text

            'Store dataset in session
            Dim stream As New System.IO.StringWriter
            dsItemsOrdered.WriteXml(stream, XmlWriteMode.DiffGram)
            Session("dsItemsOrdered") = stream
            Session("dssItemsOrdered") = dsItemsOrdered.GetXmlSchema

        End If

        gvCart.EditIndex = -1
        'DataBind()
    End Sub

    Protected Sub gvMerchandise_Command(ByVal sender As Object, ByVal e As GridViewCommandEventArgs) Handles gvMerchandise.RowCommand
        If e.CommandName = "AddToCart" Then

            'Get reference to the row being clicked on
            Dim index As Integer = e.CommandArgument
            Dim ItemID As Integer = gvMerchandise.DataKeys(index).Value
            Dim dr As DataRow = dsItemsOrdered.Tables(0).NewRow
            dr("ProductID") = ItemID
            dr("ProductName") = Me.gvMerchandise.Rows(index).Cells(0).Text
            Try
                dr("UnitPrice") = Me.gvMerchandise.Rows(index).Cells(2).Text.Substri ng(1)
            Catch ex As Exception

            End Try

            dr("Quantity") = 1
            Try
                dr("ExtendedPrice") = Single.Parse(dr("UnitPrice")) * Int16.Parse(dr("Quantity"))
            Catch ex As Exception

            End Try

            dr("booPerk") = False

            dsItemsOrdered.Tables(0).Rows.Add(dr)

            If dsItemsOrdered.Tables(0).Rows.Count <= 0 Then
                Me.lblCartEmpty.Visible = True
                divButtons.Style.Item("visibility") = "hidden"
            Else
                Me.lblCartEmpty.Visible = False
                divButtons.Style.Item("visibility") = "visible"
            End If


            'Store dataset in session
            Dim stream As New System.IO.StringWriter
            dsItemsOrdered.WriteXml(stream, XmlWriteMode.DiffGram)
            Session("dsItemsOrdered") = stream
            Session("dssItemsOrdered") = dsItemsOrdered.GetXmlSchema

            Me.gvCart.DataBind()


        End If
    End Sub

    Protected Sub btnEmptyCart_Click1(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnEmptyCart.Click
        Session("dssItemsOrdered") = Nothing
        dsItemsOrdered.Tables(0).Clear()
        Me.gvCart.DataBind()

        If dsItemsOrdered.Tables(0).Rows.Count <= 0 Then
            Me.lblCartEmpty.Visible = True
            divButtons.Style.Item("visibility") = "hidden"
        Else
            Me.lblCartEmpty.Visible = False
            divButtons.Style.Item("visibility") = "visible"
        End If

    End Sub

    Protected Sub btnCheckout_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnCheckout.Click

        'go through gridview and save all sizes to dataset so we don't lose them
        Dim i As Integer = 0
        For Each gvr As GridViewRow In Me.gvCart.Rows
            Dim DDL As DropDownList = CType(gvr.FindControl("ddlSize"), DropDownList)
            Dim selectedItem As ListItem = DDL.SelectedItem
            Dim selectedValue As String = selectedItem.Value
            dsItemsOrdered.Tables(0).Rows(i)("Size") = selectedValue
            i += 1
        Next
        dsItemsOrdered.AcceptChanges()

        'Store dataset in session
        Dim stream As New System.IO.StringWriter
        dsItemsOrdered.WriteXml(stream, XmlWriteMode.DiffGram)
        Session("dsItemsOrdered") = stream
        Session("dssItemsOrdered") = dsItemsOrdered.GetXmlSchema

        Response.Redirect("ConferenceStoreCheckout.aspx")
    End Sub

    Public Function GetSizes(ByVal ProductName As String) As DataSet
        Dim cnxn As New SqlConnection
        Dim cmd As New SqlCommand
        Dim da As New SqlDataAdapter
        Dim ds As New DataSet

        cnxn.ConnectionString = System.Configuration.ConfigurationManager.AppSetti ngs("ConnectionString")
        cnxn.Open()
        cmd.Connection = cnxn
        cmd.CommandText = "SELECT Size FROM tbl_SCGISMerchandise WHERE ProductName='" & ProductName & "'"
        da.SelectCommand = cmd

        da.Fill(ds, "Sizes")

        If ds.Tables(0).Rows(0)("Size").GetType Is System.Type.GetType("System.DBNull") Then
            Dim dr As DataRow = ds.Tables(0).NewRow
            dr("Size") = "N/A"
            ds.Tables(0).Rows.Add(dr)
        End If

        cmd.Dispose()
        da.Dispose()
        cnxn.Dispose()

        Return ds
    End Function

    Protected Sub RowDataBound(ByVal sender As Object, ByVal e As GridViewRowEventArgs) Handles gvCart.RowDataBound


    End Sub
End Class