(property owner appealed tax penalty levied against her for an impermissible change in conservation status of property under covenant agreement; property owner sold parcel of land after application approved by tax board for conservation use; board notified new owner of breach of covenant; when breach not cured, board sent notice of penalty to owner; board upheld penalty and owner appealed to court; court held law required owner to receive notice of breach and have opportunity to cure before penalty could be assessed; because owner never received first notice, penalty could not be assessed).