Hi, I remember in past there was some reports about it. And now I was a victim of this problem which is very difficult to debug. Pharo allows to start two listener sockets on same port. You will not see any error. State of both sockets will be identical. "socket isValid, socket status" will be always correct for both instances. You can play with sockets with following code: (socket := Socket newTCP) setOption: 'TCP_NODELAY' value: 1; setOption: 'SO_SNDBUF' value: 4096; setOption: 'SO_RCVBUF' value: 4096. socket listenOn: 40424 backlogSize: 32. When many listener sockets are created. Only first will receive connections. So first server will work. But others will not with no way to know why. But more dramatical scenario is when first socket becomes collected as garbage which will destroy it. In this case You will be completely confusing why your single instance in image is not working. Such case is of course some bug in how you manage sockets. But that's the problem: It is now impossible to debug such cases. Can we fix it? Is it possible to signal error when socket is not really listen? Best regards, Denis