Sorting gridview - can't find column

Sorting gridview - can't find column

Relative newbie here. Discovered that I have to write an event handler to
handle sorting of my data from an objectdatasource. Found most of what I
need, but when the code runs I get the message "Cannot find column xxx"
where xxx is the name of the column I'm trying to sort on.
I've verified that e.SortExpression is returning the proper column name. I
also verified that the datatable 'dt' is not empty. Also, I'm listing most
of the gridview definition in case that's helpful.
Protected Sub GridView1_Sorting(sender As Object, e As
GridViewSortEventArgs) Handles GridView1.Sorting
Dim dt As Data.DataTable = New Data.DataTable(GridView1.DataSource)
If Not dt Is Nothing Then
dt.DefaultView.Sort = e.SortExpression
GridView1.DataSource = dt
GridView1.DataBind()
End If
End Sub
ASPX snippet:
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
DataSourceID="ObjectDataSource1" CellPadding="4"
EmptyDataText="No records found for your search" ForeColor="#333333"
GridLines="None" Width="930px" BorderColor="#CCCCCC"
Font-Size="12px" AllowSorting="True">
<AlternatingRowStyle BackColor="White" ForeColor="#284775" />
<Columns>
<asp:BoundField DataField="CustName" HeaderText="CustName"
SortExpression="CustName" />
<asp:BoundField DataField="CustType" HeaderText="CustType"
SortExpression="CustType"
HeaderStyle-HorizontalAlign="Center"
ItemStyle-HorizontalAlign="Center" />
<asp:TemplateField HeaderText="Address" SortExpression="Addr1">
<ItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%#
Bind("Addr1") %>'></asp:Label>
</ItemTemplate>
<EditItemTemplate>
<asp:TextBox ID="TextBox1" runat="server" Text='<%#
Bind("Addr1") %>'></asp:TextBox>
</EditItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="Phone" HeaderText="Phone"
SortExpression="Phone" />
<asp:BoundField DataField="ContactName" HeaderText="ContactName"
SortExpression="ContactName" />
<asp:BoundField DataField="LastContactDate"
HeaderText="LastContact" SortExpression="LastContactDate"
dataformatstring="{0:d}" />
<asp:BoundField DataField="CustSince" HeaderText="CustSince"
SortExpression="CustSince"
dataformatstring="{0:MM/dd/yyyy}" />
<asp:BoundField DataField="Status" HeaderText="Status"
SortExpression="Status" ItemStyle-HorizontalAlign="Center"
HeaderStyle-HorizontalAlign="Center" />
<asp:BoundField DataField="Source" HeaderText="Source"
SortExpression="Source" />
<asp:BoundField DataField="RelMgr" HeaderText="RelMgr"
SortExpression="RelMgr" />
<asp:TemplateField HeaderText="RelMgrInfo">
<ItemTemplate>
<asp:HyperLink ID="RelMgrEmailLink" runat="server"
NavigateUrl='<%#Eval("RelMgrEmail", "mailto:{0}")%>'
Text='<%# Eval("RelMgrEmail") + "<br>" +
Eval("RelMgrPhone")%> '> </asp:HyperLink>
</ItemTemplate>
</asp:TemplateField>
</Columns>
Thanks!