[Twisted-Python] Reason of calling Stale Broker inside loopback

Hello, 1. What is the reason of error "DeadReferenceError: Calling Stale Broker"? My program uses PB inside loopback, so I shouldn't have any disconnects. 2. I call many time remote method returning pb.Referenceable. Can it be a reason of topic 1 or generally lead to system's degradation? Sergey.