Try this......
<RK:exporttoexcel id="ExportToExcel1" runat="server" applystyleinexcel="True" charset="utf-8" ContentEncoding="windows-1250" EnableHyperLinks="True" ExportFileName="Report.xls"
IncludeTimeStamp="True" PageSize="All" Text="Export To Excel"
PostBackUrl="Report.aspx" OnPreExport="submitButton_Click" />
set your PostBackUrl
set OnPreExport event
in OnPreExport event set GridView.DataSource and DataBind Method......
it works....