Error message

• Warning: Cannot modify header information - headers already sent by (output started at /home/sites/17b/d/d5b4d14379/public_html/includes/bootstrap.inc:1642) in drupal_send_headers() (line 1501 of /home/sites/17b/d/d5b4d14379/public_html/includes/bootstrap.inc).
• Error: Class 'Drupal\db_maintenance\Module\Hook\CommonHookHandler' not found in db_maintenance_cron() (line 36 of /home/sites/17b/d/d5b4d14379/public_html/sites/all/modules/db_maintenance/db_maintenance.module).