This could signal that a duplicate account exists. Ask the student if they have undertaken VET training after 1 January 2015. If so, it is likely to be the same student. In this case, ask the student if they have a USI. If the student can't remember their USI, they can find it via the 'Forgotten USI' function on this website.
In the event there is more than one record with similar details, please contact the USI Office.