If you come back and change your /etc/exports file, the changes you make may not take effect immediately. You should run the command exportfs -ra to force nfsd to re-read the /etc/exports file. If you can't find the exportfs command, then you can kill nfsd with the -HUP flag (see the man pages for kill for details). If that still doesn't work, don't forget to check hosts.allow to make sure you haven't forgotten to list any new client machines there
