Its a robotic gearbox? Our has the same "problem". It BEEPs two or three times and then "R"everse. I've asked technician at our local Peugeot service and he told me that this is some "protective mechanism" for clutch and gearbox, if the flywheels are not in the right position. Electronic actuator will take for some time and try in the right time to put the reverse gear IN...