> But i get nothing from the thread.
I give a try.
In  Henning Bostelmann says:
"My recommendation would be that you store your session data on the file system, not in the database" for better performance. What you have, saving in a network file system, is a different alternative, which may be the cause of your problems.
Below that in  Tim Hunt suggests:
"get your load-balancer to use sticky sessions (so all the requests from one user go to the same web server). Then you can use sessions on the server's hard disc."
> It is something about my NFS ... NAS permission.
Or rather the suitablility of network file system for session data.