Meanwhile, In a bowl, combine the achiote paste and lime juice. With a fork, stir well until mixed together. Add the shrimp and mix well to coat with the achiote mixture. In a nonstick skillet, heat 2 tablespoons of the oil. Add the shrimp and cook over moderately high heat until golden, 2 to 3 minutes; transfer to a plate. Add the butter to the skillet. Add the beans, capers and lemon juice and cook, stirring, for 2 minutes.