When adding a new starter in the system you may get the message 'National Insurance already registered' letting you know that the NI number you've entered for them is already in use.
This usually means that the person has already been created and you will be able to add the employment to the existing record rather than create a duplicate.
To resolve this:
Search for the name of the person using the search icon in the top right corner of the screen.
Click their name to go to their profile.
Click Person, then Profile.
Take a look at the NI Number field to make sure this is correct.
Take a look at the rest of the profile to ensure this is the same person you were trying to add to the system.
Click Add Additional Employment at the top of the page.
Complete all details of the employment as needed.
Click Submit.