This error displays when a performer is on authorised leave (i.e. Maternity, Paternity or Sick leave) but there is also an Net Pensionable Earnings (NPE) / Net Pensionable Earnings (NPEE) value present for their period of absence. 
The Commissioner needs to set the NPE / NPEE to zero for the period of absence.
A box shows in the NPE / NPEE field called 'Authorised Leave' if the user clicks on this it will show if the performer has authorised leave and the dates this relates to.