Exception - TCPDF ERROR: Some data has already been output, can't send PDF file

More information about this error

Debug info:

Error code: generalexceptionmessage

Stack trace:

    line 3006 of /lib/tcpdf/tcpdf.php: Exception thrown

    line 7738 of /lib/tcpdf/tcpdf.php: call to TCPDF->Error()

    line 190 of /lib/pdflib.php: call to TCPDF->Output()

    line 176 of /dataformat/pdf/classes/writer.php: call to pdf->Output()

    line 2410 of /lib/tablelib.php: call to dataformat_pdf\writer->close_output()

    line 820 of /lib/tablelib.php: call to table_dataformat_export_format->finish_document()

    line 2207 of /lib/tablelib.php: call to flexible_table->finish_output()

    line 549 of /report/log/classes/renderable.php: call to table_sql->out()

    line 182 of /report/log/index.php: call to report_log_renderable->download()

Output buffer: <br /> <b>Warning</b>: Undefined variable $username in <b>/opt/moodle/master/src/report/log/classes/table_log.php</b> on line <b>203</b><br /> <br /> <b>Warning</b>: Undefined variable $username in <b>/opt/moodle/master/src/report/log/classes/table_log.php</b> on line <b>203</b><br />