This can happen when the employee and the manager of the employee both create a timesheet for the same week commencing date.
While the system will prevent the self service user and the manager user from creating multiple timesheets with the same week commencing date, it will not prevent them from creating a single timesheet each with the same week commencing date.
The correct process is for only one of the two users to create the timesheet. If the employee submits an incorrect timesheet, the manager should reject the timesheet and ask the employee to correct and resubmit the timesheet for approval.
To delete a duplicate timesheet record, the user who created it will need to delete it via their timesheet process on their menu set.