The documentaion states that SMJobBless returns success if the service is already installed. However, if it's installed and running, SMJobBless fails and returns a code 2 (kSMErrorInternalFailure). I managed to evade the problem by forcing the helper to quit whenever a connection is invalidated or interrupted by stopping the main runloop. It's acceptable since in our case there shouldn't be two clients accessing the helper at the same time, but I still feel there's something wrong when calling SMJobBless and I can't put my finger on it... Any advice on what could go wrong and what I could try to find more about it?