I tried this code: ----------------------------------------- from twisted.spread import pb from twisted.internet import reactor class Echoer(pb.Root): def remote_echo(self, s): return s if __name__ == "__main__": reactor.listenTCP(8001, pb.PBServerFactory(Echoer())) reactor.run() ----------------------------------------- On Windows XP all is ok. On Windows 7 64 I receive this error message: ----------------------------------------- C:\Program Files (x86)\Python\lib\site-packages\twisted\spread\pb.py:30: DeprecationWarning: the md5 module is deprecated; use hashlib instead import md5 Traceback (most recent call last): File "C:\Users\bob\Documents\Twisted\pbs.py", line 11, in <module> reactor.listenTCP(8001, pb.PBServerFactory(Echoer())) File "C:\Program Files (x86)\Python\lib\site-packages\twisted\internet\posixbase.py", line 356, in listenTCP p.startListening() File "C:\Program Files (x86)\Python\lib\site-packages\twisted\internet\tcp.py", line 862, in startListening self._realPortNumber = skt.getsockname()[1] File "<string>", line 1, in getsockname socket.error: [Errno 10035] A non-blocking socket operation could not be completed immediately ----------------------------------------- What can I do?