Hm, I want to make sure I understand your issues. There is only one session here - the zk client session. there's also a network connection (the socket) btw client/server.
this message is (should be) saying that the zk client lib attempted to re-connect to the server but the client's ZK session has already expired on the server (timeout exceeded, ephemerals cleaned up, etc...) and the ZK session is no longer valid (ie the client needs to create a new session)
I'm happy to make this better (can't be much worse) but I want to make sure I grok your request.
If this log message said something like
2009-10-29 14:25:54,023 - INFO ClientCnxn - Unable to reconnect to ZooKeeper service, session 0x124a265d8b20001 has expired
would that be better? (notice info level since it's not really an error condition.)
your client watcher code is getting (in both cases) the watcher event that notifies it of the session expiration, this is a log by the client library code capturing the event.