Hi Sakshi
No, I am not using any Task chain module module in my moodle course.
You have any other solution???
When I enable Debugging. I got following extra info. about above error
Stack trace:
line 104 of /backup/util/factories/backup_factory.class.php: backup_task_exception thrown
line 124 of /backup/moodle2/backup_plan_builder.class.php: call to backup_factory::get_backup_activity_task()
line 148 of /backup/moodle2/backup_plan_builder.class.php: call to backup_plan_builder::build_activity_plan()
line 169 of /backup/moodle2/backup_plan_builder.class.php: call to backup_plan_builder::build_section_plan()
line 93 of /backup/moodle2/backup_plan_builder.class.php: call to backup_plan_builder::build_course_plan()
line 163 of /backup/util/factories/backup_factory.class.php: call to backup_plan_builder::build_plan()
line 61 of /backup/util/plan/backup_plan.class.php: call to backup_factory::build_plan()
line 336 of /backup/controller/backup_controller.class.php: call to backup_plan->build()
line 126 of /backup/controller/backup_controller.class.php: call to backup_controller->load_plan()
line 82 of /backup/backup.php: call to backup_controller->__construct()
Thanks for help.