Cenvat credit transition: unutilized credits carried forward but equivalent amounts payable when opting for exemption. Transitional rules allow unutilized CENVAT and Service Tax credits existing on 10 September 2004 to be carried forward under the 2004 Rules. Manufacturers opting for full excise exemption under notifications must pay an amount equal to the credit on inputs, input services, inputs in process or final products in stock at the time of option; after deduction any remaining credit lapses and cannot be used for duty on other goods or for export. Providers of output services face an analogous obligation when opting for full service tax exemption, with any residual credit lapsing after the requisite payment.