Problems exporting partitions via NFS

[don fisher]

I have three systems, two Ubuntu and one F14. I am trying to move to 
F14. Currently I can mount any of the Ubuntu the systems on the three 
computers. But when I try to mount the file system exported from F14 I 
receive a message from NFS:

mount.nfs: No route to host

I can ping the F14 system, so the name resolution should be ok. I use 
the same /etc/exports file on all machines, so is is probably not the 
problem.

Is there anything I need to set up with iptables, or PAM?

I am working from the command line. Any advice appreciated.

Thanks