application/vnd.ms-excel修改为application/vnd.openxmlformats-officedocument.spreadsheetml.sheet试试看
http://blogs.msdn.com/b/vsofficedeveloper/archive/2008/05/08/office-2007-open-xml-mime-types.aspx
http://blogs.msdn.com/b/vsofficedeveloper/archive/2008/05/08/office-2007-open-xml-mime-types.aspx
试了,不管用,主要是这里报错
MemoryStream ms =ExcelHelper.ExportToExcel(ds, ExcelType.Office2007, header);
建议返回memorystream,然后调用ToArray方法读取stream的内容太。