Hmmm.... not enough info to really understand problem, so this may be a stab in the dark...
I ran into a similar problem a while back. Turns out NFS was not properly configured. After entering the below commands, I was able to get NFS to work.
On the server side, enter these commands (as root):
rcmgr -c set NFSSERVING 1
rcmgr -c set NFSLOCKING 1
rcmgr -c set NFS_CONFIGURED 1
client (if a Tru64 client):
rcmgr -c set NFSLOCKING 1
rcmgr -c set NFS_NFSIOD 7
rcmgr -c set NFS_CONFIGURED 1
Then do your normal NFS exports. The NFS mount should then work.