If the walk in fridge is beeping and you see this CSD error code it probably means the condenser is blocked with dust and debris and needs a clean.
the manufacturer says -
''a quick fix for this is to brush the condenser Coil gently and carefully with the line of the aluminium fins to remove the carpet of dust off the face of the condenser, depending on the model the condenser coil this may be accessed from below or above the control panel ''