Think we found an error in the Configuring NIS Howto...
yppasswdd should NOT run on both the client & server, or you may see this error "yppasswdd not running on NIS master".
The yppasswdd daemon must be running on both the client and server for
password changes to work correctly. When they aren't running, you'll get errors.
[root@smallfry etc]# yppasswd -p nisuser
yppasswd: yppasswdd not running on NIS master host ("bigboy").