In this case the Appellate Tribunal held that according to section 2(7A) of the Act, the term “Assessing Officer” would include Joint Commissioner or Additional Commissioner, provided such Joint Commissioner or Additional Commissioner was empowered by the Board by a general or specific order authorising the Principal Chief Commissioner or Chief Commissioner or Principal Commissioner to empower the Joint Commissioner or Additional Commissioner by way of separate order under S. 120(4)(b) of the Act to act as an AO. According to the provisions of S. 120(4)(b) of the Act, the Board, might by general or special order and subject to such conditions, restrictions or limitations as might be specified therein, authorise any Principal Director General or Principal Chief Commissioner or Chief Commissioner or Principal Commissioner to issue orders in writing that the powers and functions of an AO to the Joint Commissioner or Additional Commissioner in cases of persons or classes of persons. Unless the Joint Commissioner or Additional Commissioner was empowered by the Principal Chief Commissioner or Chief Commissioner or Principal Commissioner by an order in writing to act as an AO and perform such functions, the Joint Commissioner could not act as an Assessing Officer. Admittedly, the Department had failed to file any specific order passed by the Principal Chief Commissioner or Chief Commissioner or Principal Commissioner, under S.120(4)(b), authorising the Joint Commissioner to act as an AO in the case of the assessee. Although the Department had filed a copy of the Board general notification authorising the Joint Commissioner or Additional Commissioner to act as an Assessing Officer, it failed to file any order of the Principal Commissioner under S. 120(4)(b) of the Act empowering the Joint Commissioner to act as an Assessing Officer. Although the Department had filed order of the Principal Commissioner passed under S.120(1) and (2) of the Act, the order was not under S.120(4)(b) of the Act. Therefore, the reassessment order passed by the Joint Commissioner was void ab initio and liable to be quashed because the Assessing Officer who had passed the reassessment order had no valid jurisdiction and authority to pass such order, in the absence of proper order in writing under S. 120(4)(b) of the Act. (AY. 2006-07, 2007-08)