Itr 4 defective return notice under sec139 (9) with error code 31

My friend is a professional, so he has been filing ITR-4 form for the last few years. His professional income is less than Rs 2.5 Lakhs after deducting tds under sec 194 j and hence it is not required to audit his accounts. There is no necessity for him to provide full details of Balance sheet in ITR. He choose the option no for sec 44A & 44AB . But in this year income tax dept return the ITR with defect under sec 139 ( 9 ). What is the solution of this defect.