Exit 12 error

[reader at newsguy.com]

rsync  version 2.6.9cvs  protocol version 29
Running rsync from an rsnapshot script I get the following error:

  unknown message 4:1 [generator]
  rsync error: error in rsync protocol data stream (code 12) at io.c(307) [generator=2.6.9cvs]
  rsync: connection unexpectedly closed (1718 bytes received so far) [sender]
  rsync error: error in rsync protocol data stream (code 12) at io.c(453) [sender=2.6.9cvs]

Rsync was called with these flags
   -vva  --delete  --numeric-ids  --links  \
   --delete-excluded --stats   /etc/    /bk/etc/

Exit 12 information in `man rsync' isn't very helpfull.  At least to a
layman.

Can Anyone shed some light on this?