Problem with Gridview Export to Excel

I have a Gridview designed like this:
<asp:GridView ID="GridView1" runat="server" DataKeyNames="member_id" AutoGenerateColumns="False" AllowSorting="True" CssClass="dgrid" DataSourceID="SqlDataSource1"> <HeaderStyle CssClass="dgridheader"/> <Columns> <asp:BoundField DataField="site_id" HeaderText="site_id" Visible="true" /> <asp:BoundField DataField="Name" HeaderText="Business" SortExpression="Name" /> <asp:BoundField DataField="housenumber" HeaderText="Housenumber" SortExpression="housenumber" /> <asp:BoundField DataField="Address" HeaderText="Street" SortExpression="address, housenumber, address2" /> <asp:BoundField DataField="address2" HeaderText="Unit" /> <asp:BoundField DataField="city" HeaderText="City" SortExpression="city" /> <asp:BoundField DataField="State" HeaderText="State" SortExpression="state" /> <asp: ...