[tlug] "mount system call failed"

[Dave M G <dave@example.com>]

TLUG,

This error has come completely out of the blue. All my networked 
computers were working fine up until a day ago. I haven't changed 
anything - so far as I know - with network settings or anything related.
One of my computers now won't connect.

I have a Mythbuntu computer I leave on 24/7. And I have a work computer 
I turn on when needed. When I boot the work computer, it has always just 
automatically connected to the Mythbuntu computer using NFS.
Here is the /etc/fstab entry:
# Mythbuntu
192.168.0.4:/home/media /home/dave/Mythbuntu nfs 
rsize=8192,wsize=8192,timeo=14,intr
When I try a mount -a command, it takes a bunch of time then gives this 
unhelpful response:
$ sudo mount -a
[sudo] password for dave:
mount.nfs: mount system call failed

This started yesterday, and I rebooted both computers a few times, and 
eventually it worked, so I thought maybe it was just some setting.
However, today, no matter what order I boot the computers, the network 
won't connect. Both can see the internet, and my work computer connects 
to my Windows machine (SAMBA) fine. The problem seems to just be between 
these two.
I tried looking the mount error up, but most posts on the topic I found 
were just as mystified as I am.
Any idea what to do to diagnose this problem?

Any advice would be much appreciated.

--
Dave M G