When accessing calendar:

Debug info: SELECT id FROM {user} WHERE id = ? AND deleted = ?
[array (
0 => '15',
1 => 0,
)]
Error code: invaliduser

Stack trace:

• line 1599 of /lib/dml/moodle_database.php: dml_missing_record_exception thrown
• line 1575 of /lib/dml/moodle_database.php: call to moodle_database->get_record_select()
• line 6496 of /lib/accesslib.php: call to moodle_database->get_record()
• line 133 of /calendar/classes/external/events_related_objects_cache.php: call to context_user::instance()
• line 197 of /calendar/classes/external/day_exporter.php: call to core_calendar\external\events_related_objects_cache->get_context()
• line ? of unknownfile: call to core_calendar\external\day_exporter->core_calendar\external
  {closure}()
• line 210 of /calendar/classes/external/day_exporter.php: call to array_map()
• line 101 of /calendar/classes/external/week_day_exporter.php: call to core_calendar\external\day_exporter->get_other_values()
• line 125 of /lib/classes/external/exporter.php: call to core_calendar\external\week_day_exporter->get_other_values()
• line 164 of /calendar/classes/external/week_exporter.php: call to core\external\exporter->export()
• line 125 of /lib/classes/external/exporter.php: call to core_calendar\external\week_exporter->get_other_values()
• line 312 of /calendar/classes/external/month_exporter.php: call to core\external\exporter->export()
• line 215 of /calendar/classes/external/month_exporter.php: call to core_calendar\external\month_exporter->get_weeks()
• line 125 of /lib/classes/external/exporter.php: call to core_calendar\external\month_exporter->get_other_values()
• line 3477 of /calendar/lib.php: call to core\external\exporter->export()
• line 146 of /calendar/view.php: call to calendar_get_view()

When accessing a particular course (Rest of courses are working.):

Debug info: SELECT id FROM {user} WHERE id = ? AND deleted = ?
[array (
0 => '15',
1 => 0,
)]
Error code: invaliduser

Stack trace:

• line 1599 of /lib/dml/moodle_database.php: dml_missing_record_exception thrown
• line 1575 of /lib/dml/moodle_database.php: call to moodle_database->get_record_select()
• line 6496 of /lib/accesslib.php: call to moodle_database->get_record()
• line 133 of /calendar/classes/external/events_related_objects_cache.php: call to context_user::instance()
• line 117 of /calendar/classes/external/calendar_upcoming_exporter.php: call to core_calendar\external\events_related_objects_cache->get_context()
• line ? of unknownfile: call to core_calendar\external\calendar_upcoming_exporter->core_calendar\external {closure}

  ()

• line 137 of /calendar/classes/external/calendar_upcoming_exporter.php: call to array_map()
• line 125 of /lib/classes/external/exporter.php: call to core_calendar\external\calendar_upcoming_exporter->get_other_values()
• line 3486 of /calendar/lib.php: call to core\external\exporter->export()
• line 53 of /blocks/calendar_upcoming/block_calendar_upcoming.php: call to calendar_get_view()
• line 341 of /blocks/moodleblock.class.php: call to block_calendar_upcoming->get_content()
• line 235 of /blocks/moodleblock.class.php: call to block_base->formatted_contents()
• line 1181 of /lib/blocklib.php: call to block_base->get_content_for_output()
• line 1233 of /lib/blocklib.php: call to block_manager->create_block_contents()
• line 374 of /lib/blocklib.php: call to block_manager->ensure_content_created()
• line 3966 of /lib/outputrenderers.php: call to block_manager->region_has_content()
• line 40 of /theme/moove/layout/course.php: call to core_renderer->blocks()
• line 1374 of /lib/outputrenderers.php: call to include()
• line 1304 of /lib/outputrenderers.php: call to core_renderer->render_page_layout()
• line 244 of /course/view.php: call to core_renderer->header()