Some users collide with such mistake at creation of a backup copy:
"A required parameter (backup_unique_code) was missing"
This mistake appears at use dbsession. At a stage "check" the information is not kept in session because the limit "max_allowed_packet" in MySQL is exceeded.
Unfortunately, Moodle in any way does not process this mistake and does not notify on its reason.
- has been marked as being related by
MDL-26769 Need environment checks for : freetds or other installation must have DB/connectors text size set to a 20971520 to avoid errors with DB