Assessing Officer rejected valuation of closing stock by assessee for non-production of stock register and estimated it on basis of gross profit margin. Assessee submitted that with assessment having been completed under section 143(3) and after assessee had produced its books of account, question of invoking section 145 did not arise. CIT(A) and Tribunal affirmed the order of the Tribunal. On appeal the Court held that since in rejecting assessee’s books of account under section 145 a serious error was committed, order of Assessing Officer was to be set aside. (AY. 2005-06)