rsync - Nov 2003 - error in socket IO (code 10)

I'm getting the error:
   rsync error: error in socket IO (code 10) at 
/SourceCache/rsync/rsync-11/rsync/clientserver.c(83)

This is on OSX 10.3.1 running rsync "version 2.5.6  protocol version 
26".
And the same for the rsync server.

Any suggestions?

-- Steve