what causes Oil indicator light and message of 'No oil pressure - stop engine ASAP'

Low oil pressure, most likely due to leaking seals in the oil pan. These seals are what seals the oil pressure passageway from the pump to the engine, when they leak (which is very common) these symptoms will occur. Removal of the oil pan will be needed to address this, but have a shop perform the basic checks first to make sure everything else is OK.