水晶报表WEBFORM导出问题

我以HELP中的方法实现:
private void Button1_Click(object sender, System.EventArgs e)
{
CrystalReport1 myreport = new CrystalReport1();
ExportOptions exportOpts = new ExportOptions();
DiskFileDestinationOptions diskops = new DiskFileDestinationOptions();
exportOpts = myreport.ExportOptions;
exportOpts.ExportDestinationType=ExportDestinationType.DiskFile;
exportOpts.ExportFormatType=ExportFormatType.Excel;
diskops.DiskFileName="c:\\download.xls";
exportOpts.DestinationOptions=diskops;
myreport.Export();
}
结果在执行myreport.Export();时出现错误:
[LoadSaveReportException: 文件 C:\WINDOWS\TEMP\temp_f1be980f-8200-4509-8d8b-7c45d61b083a.rpt 内出错：
拒绝访问报表文件。其他程序可能正在使用它。]