Error in RPC subsystem

[root at peach.eas.asu.edu]

Hello;
	I'm attempting to use nis+ (nis-utils-1.4.1) on Redhat 6.2. 
It works for two of the clients, but three others give the error 
"Error in RPC subsystem"  as I said I've read the archive so yes
the clocks are with in seconds of each other.  What else may cause
that error?

Thanks
Scott