I am trying to approve a timesheet but am getting the error message that there is an overlapping timesheet, why is this?

This is because the candidate has already submitted a timesheet that has a time period overlapping with the timesheet that you are trying to approve. Candidates cannot submit overlapping timesheets therefore it is likely that you have updated a detail on the timesheet and this has caused the overlap. Please review the other timesheets submitted by the candidate to identify where the overlap is to prevent any errors in overpayment.