I see the following error quite frequently in my debug-list.
#1 ERROR: Error: Undefined index: download in '/var/www/<security edit>/httpdocs/application/controllers/ToolController.class.php' on line 207 (error code:
#2 ERROR: Error: Undefined index: lang in '/var/www/<security edit>/httpdocs/application/controllers/ToolController.class.php' on line 215 (error code:
Sometimes it's only the line 207 error, see the attached error-log.
Maybe a suggestion for development: to have a php-script to where you can upload debug-logs and let it sort errors on frequency in a database, so the devs can quickly see common bugs.