File locking is not working on 6.x and FCFSHA 5.1Sp1 for NFS.
Oct 29 07:19:26 servername rpc.mountd: authenticated unmount request from ip-address for /export/data25 (/export/data25)
Oct 29 07:23:40 servername rpc.statd: Failed to insert: creating /var/lib/nfs/statd/sm/techradl16.rad.com: Permission denied
Oct 29 07:23:40 servername rpc.statd: STAT_FAIL to servername for SM_MON of ip-address
Oct 29 07:23:40 servername kernel: lockd: cannot monitor techradl16
Both the sm and sm.bak links for rhel6 are owned by root and not rpcuser.
Once ownership is changed to 'rpcuser' this works.
# cat etc/redhat-release
Red Hat Enterprise Linux Server release 6.3 (Santiago)
# grep vx rpm_aq