ORA 22 invalid session id; access denied

My colleage was badly struck with the 'ORA 22 invalid session id; access denied'  

problem while connecting to any database from an AIX machine (where Oracle client was installed).

All the links including ML note to this errors, never helped to resolve the issue.

In our case, the problem occured because the hostname of this machine was mentioned wrongly in the /etc/hosts file.

Once we corrected the hostname in the hosts file, problem has been resolved.

Regards,

Jaffar