The reason why you get this error message is because there's an employee who has a pay record already on that day and there can't be two on the same day. You'll need removing from the file as it was manually updated.
To find the error, follow the below steps:
Click Configuration then click Data Manager.
Click Data Imported then click Imported.
This then shows the error on the right-hand side next to the upload, you'll need to remove the employee from the upload or the existing salary on that date removed.