Don’t we love IE? 🙂
Try using those headers:
header("Pragma: public");
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: private",false);
header("Content-Type: application/octet-stream");
header("Content-Disposition: attachment; filename=\"exportevent.csv\";" );
header("Content-Transfer-Encoding: binary");
I think that the octet-stream content type forces IE to download the file.