IITR.000660 as set by the ATO states that:
'When a positive Gross income amount has been provided for a Salary or Wages payment summary, either the Payer's Australian business number or Payer's - Withholder payer number must be provided.'
As such if you have a positive amount in the Gross income field but no Payer's Australian business number or Payer's - Withholder payer number then this error will trigger as per the ATO instructions.
The only way to resolve this error is to either provide the Payer's Australian business number or Payer's - Withholder payer number or you will need to remove the amount at Gross Income. There is no other way to resolve this error based on the ATO instructions.
If you do not feel that this is the case with your specific return you will need to contact the ATO, provide them with the situation, error code and message and they may be able to advise you on how to circumvent this error in this specific instance.