rsync error: timeout in data send/receive (code 30) at /home/lapo/packaging/tmp/rsync-2.6.3/io.c(153)

We are rsync'ing from an xp box running cygwin to a redhat box, using a Perl script that fist calls for an ssh tunnel, then calls rsync through local host.

ssh -P -f -L 8740:remote.host.ip:873 user@firewall.ip -p 22 sleep 25

rsync -vrtz -v --timeout=180 --exclude-from=exludefiles rsync://localhost:8740/<remote path>   <target path>
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This has worked for quite a while on a daily cron job.  We can still open the ssh tunnel without any problem.  After the tunnel is open and we run rsync, we get the following error messages:

rsync error: timeout in data send/receive (code 30) at /home/lapo/packaging/tmp/rsync-2.6.3/io.c(153)
rsync: connection unexpectedly closed (598306 bytes read so far)
rsync error: error in rsync protocol data stream (code 12) at io.c(165)
rsync: connection unexpectedly closed (598306 bytes read so far)
rsync error: error in rsync protocol data stream (code 12) at io.c(165)
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Then it returns to the command prompt.  The number of 'bytes read so far' is not constant on the different times we've tried rsync'ing, but this number does stay around 590kB.

Does anybody have any ideas?