When reverting a secondment, the employee cannot have a salary line already created on the date of the secondment's return date.
If you receive the message 'Cannot add two salaries on same day - matched against Employment type...' you will need to first delete the existing line and then revert the secondment.
Search for the employee and go to their profile.
Click Payroll, then Pay.
Click Pay History.
Click the line with the effective date of the secondment's end date.
Click Delete.
You may see a pop-up message letting you know that you cannot delete this line as it's in use, but if you refresh the browser page the line will be deleted.
Go to Employment and click Position.
Click Revert Secondment.
Make sure the date in the Return Date field is correct and click Return Secondment.