Prior Period Expense Disallowance

Suppose a Company omitted to account for an expense by mistake (assume it is not subject to TDS) in the previous year 2008/09. Company accounted that expense Rs.1000  in the subsequent previous year 2009/10 as prior period expense. While computing the taxable income of the previous year 2009/10, is that amount of Rs.1000, an allowable expense? or if it is to be disallowed, under which section of the Act it is done so? please help...Thank U!