My crystal ball is cracked so everything is fuzzy! So to SWAG;
You should check your '/etc/hosts', '/etc/hosts.allow', and '/etc/hosts.deny'. Don't forget your '/etc/exports' file. Whenever you want to change be sure to update the exportfs.
excerpt from 'man exportfs';
exportfs - maintain list of NFS exported file systems
/usr/sbin/exportfs [-avi] [-o options,..] [client:/path ..]
/usr/sbin/exportfs -r [-v]
/usr/sbin/exportfs [-av] -u [client:/path ..]
The exportfs command is used to maintain the current table of exported
file systems for NFS. This list is kept in a separate file named
/var/lib/nfs/xtab which is read by mountd when a remote host requests
access to mount a file tree, and parts of the list which are active are
kept in the kernel's export table.
Normally this xtab file is initialized with the list of all file sys-
tems named in /etc/exports by invoking exportfs -a.