Get Old Gridview Row Values In The RowUpdating Event

How do I get the old values in a gridview row in the row_updating event? I'm using a sqldatasource control to populate the grid and want to write the update code in the RowUpdating event. There are 10 fields displayed in the grid. I can get the value of the first field using string old_Category = e.OldValues[0].ToString();.

But it doesn't work for index items greater than 0. This doesn't work string old_Category = e.OldValues[1].ToString(); it returns an error message Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index. even though there are 10 columns in the grid.

<asp:GridView
ID="GridView1"
runat="server"
AutoGenerateColumns="False"
DataSourceID="SqlDataSource1"
BorderWidth="0px"
BorderStyle="None"
Width="100%"
CellPadding="2"
PageSize="25"
OnRowDeleting="ProjectListGridView_RowDeleting"
onrowdatabound="GridView1_RowDataBound"
onrowupdating="GridView1_RowUpdating" onrowediting="GridView1_RowEditing" >
<Columns>
<asp:CommandField ShowEditButton="True" />
<asp:TemplateField HeaderText="WeekEnding" SortExpression="WeekEnding">
<ItemTemplate>
<asp:Label ID="lblWeekEnding" runat="server" Text='<%# Bind("WeekEnding") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Project" SortExpression="Project">
<EditItemTemplate>
<asp:DropDownList
ID="DropDownList1"
runat="server"
DataSourceID="sdsDdlProjectsEdit"
DataTextField="ProjectName"
DataValueField="ProjectID"
AutoPostBack="True" onselectedindexchanged="DropDownList1_SelectedIndexChanged"
>
</asp:DropDownList>
<asp:SqlDataSource
ID="sdsDdlProjectsEdit"
runat="server"
ConnectionString="<%$ ConnectionStrings:ttuser %>"
SelectCommand="SELECT ProjectID,ProjectName FROM dbo.aspnet_starterkits_Projects">
</asp:SqlDataSource>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Bind("Project") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Category" SortExpression="Category">
<EditItemTemplate>
<asp:DropDownList
ID="DropDownList2"
runat="server"
DataSourceID="sdsDDL2"
DataTextField="CategoryName"
DataValueField="CategoryID">
</asp:DropDownList>
<asp:SqlDataSource
runat="server"
ID="sdsDDL2"
ConnectionString="<%$ ConnectionStrings:ttuser %>"
SelectCommand="SELECT [CategoryID], [CategoryName],[ProjectID] FROM dbo.aspnet_starterkits_ProjectCategories WHERE ([ProjectID]=@ProjectID)">
<SelectParameters>
<asp:Parameter Name="ProjectID" />
</SelectParameters>
</asp:SqlDataSource>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label2" runat="server" Text='<%# Bind("Category") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Sun" SortExpression="Sun">
<EditItemTemplate>
<asp:TextBox ID="txtSunEdit" runat="server" Text='<%# Eval("Sun") %>' Columns="2"></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="lblSun" runat="server" Text='<%# Bind("Sun") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Mon" SortExpression="Mon">
<EditItemTemplate>
<asp:TextBox ID="txtMonEdit" runat="server" Text='<%# Eval("Mon") %>' Columns="2"></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label4" runat="server" Text='<%# Bind("Mon") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Tue" SortExpression="Tue">
<EditItemTemplate>
<asp:TextBox ID="txtTueEdit" runat="server" Text='<%# Eval("Tue") %>' Columns="2"></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label5" runat="server" Text='<%# Bind("Tue") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Wed" SortExpression="Wed">
<EditItemTemplate>
<asp:TextBox ID="txtWedEdit" runat="server" Text='<%# Eval("Wed") %>' Columns="2"></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label6" runat="server" Text='<%# Bind("Wed") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Thu" SortExpression="Thu">
<EditItemTemplate>
<asp:TextBox ID="txtThuEdit" runat="server" Text='<%# Eval("Thu") %>' Columns="2"></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label7" runat="server" Text='<%# Bind("Thu") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Fri" SortExpression="Fri">
<EditItemTemplate>
<asp:TextBox ID="txtFriEdit" runat="server" Text='<%# Eval("Fri") %>' Columns="2"></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label8" runat="server" Text='<%# Bind("Fri") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Sat" SortExpression="Sat">
<EditItemTemplate>
<asp:TextBox ID="txtSatEdit" runat="server" Text='<%# Eval("Sat") %>' Columns="2"></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label9" runat="server" Text='<%# Bind("Sat") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
and here is the sqldatasource
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="<%$ ConnectionStrings:ttuser %>"
SelectCommand="SELECT
@WeekEnding WeekEnding
,Project
,ProjectID
,Category
,CategoryID
,isnull([1], 0) Sun
,isnull([2], 0) Mon
,isnull([3], 0) Tue
,isnull([4], 0) Wed
,isnull([5], 0) Thu
,isnull([6], 0) Fri
,isnull([7], 0) Sat
from
(select P.ProjectName Project,P.ProjectID, CAT.CategoryName Category,CAT.CategoryID, Datepart(dw, TE.TimeEntryDate) DOW, TE.TimeEntryDuration Hours
FROM
dbo.aspnet_starterkits_TimeEntry TE inner join
dbo.aspnet_starterkits_ProjectCategories CAT on
TE.CategoryID=CAT.CategoryID inner join
dbo.aspnet_starterkits_Projects P on
CAT.ProjectID=P.ProjectID
Where (TE.TimeEntryDate between dateadd(dd, -6, @WeekEnding) and @WeekEnding) AND
TE.TimeEntryUserID=(SELECT UserId FROM dbo.aspnet_Users WHERE UserName=@UserName)) Source
pivot (max(Hours)for DOW in ([1],[2],[3],[4],[5],[6],[7]) ) as pvt" OldValuesParameterFormatString="original_{0}"
<SelectParameters>
<asp:ControlParameter ControlID="WeekEnding2" Name="WeekEnding"
PropertyName="Text" />
<asp:ControlParameter ControlID="UserList" Name="UserName"
PropertyName="SelectedValue" />
</SelectParameters>
</asp:SqlDataSource>