The only way I know to do it is start over.  In my shop its usually caused
by the LAN group changing switches and such without telling me.
First check to see if you can ping IP addresses from the host out to the
client and the client to the host.  Also, check if your cards are ok at the
clients as well as the host.
If the above checks out the client probably loss the password and you will
need to reestablish it.
That would be my suggestions.

Have you done any upgrades lately of AIX or other?

Philip A. James, Systems Software Specialist
Software Services Unit
Information Technology Services Division / Data Center
California Public Employees' Retirement System
Phone: (916) 326-3715
Fax:     (916) 326-3884
Email:  phil_james AT calpers.ca DOT gov