by Karikalan Kumaresan.
Similar issue for me. I changed the
$worksheet[0] = $workbook->add_worksheet('');
to
$worksheet[0] = $workbook->add_worksheet('export');
in moodle/admin/user_bulk_download.php, which resolved this error and downloads the excel file, however I could not open the downloaded file as it says that the "file may have been corrupted". Any help would be greatly appreciated.
Thanks,
Kari...