"In general, correction of an operational error requires the plan sponsor to put the plan and the participants in the position they would have been if the error had not occurred. If the correction requires the plan sponsor to amend the plan, the [EPCRS] generally requires the plan to file under the Voluntary Correction Program (VCP). However, EPCRS provides five situations in which a plan sponsor may adopt a retroactive corrective amendment under the Self-Correction Program (SCP) and not have to file under VCP."