A Google search turned up
http://lists.insecure.org/linux-kernel/2001/Dec/5052.html:

  "Basically it means that your rpc.statd daemon is unaware of a lot
   of its clients. It is probably failing to save their IP-numbers
   to disk. Check therefore that the directories /var/lib/nfs/sm, and
   /var/lib/nfs/sm.bak (or /var/lib/nfs/statd/sm, ... on some platforms)
   are writable by the rpc.statd process."

On Mon, 30 Sep 2002, Hanasaki JiJi wrote:

> The below has been showing up lately in the syslog of the NFS Server 
> box.  Any thoughts on what could cause this?  How to fix it?  Nothing in 
> the config has changed in quite some time (neither client nor server)
> 
> Debian Woody - Kernel 2.4.19
> 
> rpc.statd[269]: Received erroneous SM_UNMON request from [host] for [ip]
> 
> 
> 
>