This error can occur in two scenarios:
PC or Terminal Services session may have crashed, causing timesheets to log out, close incorrectly.
User Closed out of timesheets and it did not update the database effectively.
Open Timesheet Administration.
Select the correct week of the month.
On the right hand side of the Timesheet Administration screen check if the user has a red or white padlock:
Red Padlock: an invalid log.
White Padlock: Timesheets are currently open.Right click on the red lock and select Remove Timesheet Log from the context menu.
This will remove the invalid log and the user will be able to access the timesheet for that specific week.