RPC error when umounting an NFS mount point

[James D. Parra]

Hello,

We have one server hosting the home directories via an NFS share for all the
other Linux boxes. We needed to reboot the system and when attempting to
"umount -f" the NFS /home shares on the other machines we get the following
error;

Cannot MOUNTPROG RPC: RPC: Port mapper failure - RPC: Unable to receive
umount: 


How can we unmount this NFS share without rebooting the systems? Some
machines actually hang on the RPC indefinitely during shutdown.

Thank you in advance,

James